Cancellation of interference in a communication system with application to S-CDMA

ABSTRACT

A relatively straight-forward implemented, and computationally efficient approach of selecting a predetermined number of unused codes is used to perform weighted linear combination selectively with each of the input spread signals in a multiple access communication system. If desired, the predetermined number of unused codes is always the same in each implementation. Alternatively, the predetermined number of unused codes are selected from within a reordered code matrix using knowledge that is shared between the two ends of a communication system, such as between the CMs and a CMTS. While the context of an S-CDMA communication system having CMs and a CMTS is used, the solution is generally applicable to any communication system that seeks to cancel narrowband interference. Several embodiments are also described that show the generic applicability of the solution across a wide variety of systems.

CROSS REFERENCE TO RELATED PATENTS/PATENT APPLICATIONS

The present U.S. Utility Patent Application claims priority pursuant to35 U.S.C. § 119(e) to the following U.S. Provisional Patent Applicationswhich are hereby incorporated herein by reference in their entirety andmade part of the present U.S. Utility Patent Application for allpurposes:

1. U.S. Provisional Application Ser. No. 60/151,680, entitled“Subdimensional single carrier modulation,” filed Aug. 31, 1999,pending.

2. U.S. Provisional Application Ser. No. 60/367,564, entitled“Cancellation of interference in a communication system with applicationto S-CDMA,” filed Mar. 26, 2002, pending.

The present U.S. Utility Patent Application also claims prioritypursuant to 35 U.S.C. § 120 to the following U.S. Utility Applicationwhich is hereby incorporated herein by reference in its entirety andmade part of the present U.S. Utility Patent Application for allpurposes:

1. U.S. Utility application Ser. No. 09/652,721, entitled“Subdimensional single carrier modulation,” filed Aug. 31, 2000,pending, which claims priority pursuant to 35 U.S.C. § 119(e) to U.S.Provisional Application Ser. No. 60/151,680, entitled “Subdimensionalsingle carrier modulation,” filed Aug. 31, 1999, Utility PatentApplication for all purposes.

TECHNICAL FIELD OF THE INVENTION

The invention relates generally to communication systems; and, moreparticularly, it relates to communication systems that may be affectedby undesirable interference.

BACKGROUND OF THE INVENTION

Signal processing within communication systems having a communicationchannel, in an effort to improve the quality of signals passing throughthe communication channel, has been under development for many years. Inthe past several years, emphasis has moved largely to the domain ofdigital communication systems that modulate bit streams into an analogsignal for transmission over a communication channel. This channel canbe a variety of channel types. Many different approaches are employed inthe prior art to try to minimize or substantially reduce the effects ofinterference that may be introduced into a signal that is transmittedacross a communication channel. In particular, the prior art approachesthat seek to perform cancellation of interference that occupies a smallnumber of signal dimensions in a signal are typically deficient for anumber of reasons as is briefly referenced below. One particular type ofinterference that these prior art schemes seek to minimize is thenarrowband interference that is sometimes referred to as ingressinterference. Another type of narrowband interference that may beproblematic is the interference of impulse/burst noise. Yet another typeof interference that may be problematic is within the code divisionmultiple access (CDMA) context when the interference is on a smallnumber of codes.

One of the main methods employed in the prior art to eliminate thisinterference is the use of a notch filter. This solution is sufficientin some applications, but the notch filter itself oftentimes causesdistortion of the desired signal. In the CDMA context, this distortionis called inter-code interference (ICI). Then, another means mustoftentimes be included to remove the very ICI that has been introducedby the notch filter. One way to do this is to de-spread the signal.Then, hard decisions are made using the de-spread signal. The harddecisions are then respread and passed through a copy of the notchfilter. The difference between input and output of this filterrepresents an estimate of the distortion introduced by notching outinterference and can be used to remove this distortion. In someinstances, this process is repeated several times to achieve an adequateresult. Making hard decisions involves the possibility of decisionerrors. Many iterations may be required to achieve convergence tocorrect decisions, if convergence to an error-free situation occurs atall.

These prior art approaches described above are deficient in that theysuffer the effect of error propagation. The decision circuit is prone tomake incorrect decisions, requiring many iterations before the processconverges, if it ever converges at all.

Further limitations and disadvantages of conventional and traditionalsystems will become apparent through comparison of such systems with theinvention as set forth in the remainder of the present application withreference to the drawings.

BRIEF SUMMARY OF THE INVENTION

Various aspects of the invention can be found in a communicationreceiver that supports interference cancellation functionality. Thepresent invention uses a linear combination of the unused dimensions(for example, the unused codes) to cancel the interference. This may bedone after the de-spreader, or, equivalently, as part of thede-spreading process. There is no appreciable inter-code interferenceintroduced and no decision errors are made as part of this process. Theallocation of unused codes reduces the capacity of the system by a smallamount. In one embodiment, the reduction of capacity of the system willbe to 120/128 of the original capacity for a system of 128 codes where 8unused codes are employed. Clearly, other numbers of available codes mayalso be employed without departing from the scope and spirit of theinvention.

It is noted that the present invention may be extended across a widevariety of application contexts. The present technique can be applied tocancel not only narrowband interference, but any interference thatoccupies a small number of dimensions in the signal space. Thenarrowband interference includes just one of the many types ofinterferences that may be substantially cancelled according to thepresent invention. A narrowband signal occupies a small number of DFT(discrete Fourier transform) bins, showing that it occupies a smallnumber of dimensions in signal space. An extremely simple example is aCW (Continuous Wave) signal whose frequency is an integer multiple ofthe de-spread symbol rate; this CW signal occupies only a single bin inthe DFT, or only one dimension in the signal space, where each dimensionis, in this case, one DFT bin. Another example is a short burst of noise(impulse or burst noise). A short burst signal occupies a small numberof time samples, again showing that it too occupies a small number ofdimensions, where each dimension is, in this case, a time sample.

Other types of signals may be constructed, without limit, that satisfythe property that they occupy a small number of dimensions in theirrespective signal space. All such signals can be canceled by the presenttechnique. It is noted that the DFT is just one example of anorthonormal expansion. A second example is the code matrix in DOCSIS 2.0S-CDMA. A third example may be the identity matrix. Innumerable otherorthonormal transforms also exist that are used to transform a signal ina finite signal space. If a signal occupies a small number of dimensionsin any orthonormal transformation, the interference cancellationperformed according to the present invention may be used for cancelingit. It is noted here that orthogonal transformations may also be usedwithout departing from the scope and spirit of the invention in any way.

A number of specific embodiments are illustrated to show the versatilityand wide applicability of the present invention across a variety ofcommunication systems contexts. However, it is generally noted that thepresent invention may be practiced within any communication system thatseeks to perform interference cancellation when the communication systememploys signaling that occupies fewer dimensions in the communicationsignal's space than available in this space.

The present invention is directed to apparatus and methods of operationthat are further described in the following Brief Description of theSeveral Views of the Drawings, the Detailed Description of theInvention, and the claims. Other features and advantages of the presentinvention will become apparent from the following detailed descriptionof the invention made with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

A better understanding of the invention can be obtained when thefollowing detailed description of various exemplary embodiments isconsidered in conjunction with the following drawings.

FIG. 1 is a system diagram illustrating an embodiment of a cable modem(CM) communication system that is built according to the presentinvention.

FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system that is built according to the present invention.

FIG. 3A is a system diagram illustrating an embodiment of a cellularcommunication system that is built according to the present invention.

FIG. 3B is a system diagram illustrating another embodiment of acellular communication system that is built according to the presentinvention.

FIG. 4 is a system diagram illustrating an embodiment of a satellitecommunication system that is built according to the present invention.

FIG. 5A is a system diagram illustrating an embodiment of a microwavecommunication system that is built according to the present invention.

FIG. 5B is a system diagram illustrating an embodiment of apoint-to-point radio communication system that is built according to thepresent invention.

FIG. 6 is a system diagram illustrating an embodiment of a highdefinition (HDTV) communication system that is built according to thepresent invention.

FIG. 7 is a system diagram illustrating an embodiment of a communicationsystem that is built according to the present invention.

FIG. 8 is a system diagram illustrating another embodiment of acommunication system that is built according to the present invention.

FIG. 9 is a system diagram illustrating an embodiment of a cable modemtermination system (CMTS) system that is built according to the presentinvention.

FIG. 10 is a system diagram illustrating an embodiment of a burstreceiver system that is built according to the present invention.

FIG. 11 is a system diagram illustrating an embodiment of a single chipDOCSIS/EuroDOCSIS CM system that is built according to the presentinvention.

FIG. 12 is a system diagram illustrating another embodiment of a singlechip DOCSIS/EuroDOCSIS CM system that is built according to the presentinvention.

FIG. 13 is a system diagram illustrating an embodiment of a single chipwireless modem system that is built according to the present invention.

FIG. 14 is a system diagram illustrating another embodiment of a singlechip wireless modem system that is built according to the presentinvention.

FIG. 15 is a diagram illustrating an embodiment of a vector de-spreaderthat is built according to the present invention.

FIG. 16 is a diagram illustrating an embodiment of an interferencecanceler that is built according to the present invention.

FIG. 17 is a diagram illustrating another embodiment of an interferencecanceler that is built according to the present invention.

FIG. 18 is a diagram illustrating another embodiment of an interferencecanceler that is built according to the present invention.

FIG. 19 is a diagram illustrating an embodiment of an interferencecanceler with memory that is built according to the present invention.

FIG. 20 is a diagram illustrating an embodiment of equalization withcanceler that is arranged according to the present invention.

FIG. 21 is a diagram illustrating an embodiment of Least Means Square(LMS) training of an interference canceler according to the presentinvention.

FIG. 22A is a diagram illustrating an embodiment of signaltransformation according to the present invention.

FIG. 22B is a diagram illustrating another embodiment of signaltransformation according to the present invention.

FIG. 23 is an operational flow diagram illustrating an embodiment of aninterference cancellation method that is performed according to thepresent invention.

FIG. 24 is an operational flow diagram illustrating another embodimentof an interference cancellation method that is performed according tothe present invention.

FIG. 25 is an operational flow diagram illustrating an embodiment of anunused code selection method that is performed according to the presentinvention.

FIG. 26 is an operational flow diagram illustrating an embodiment of anS-CDMA interference cancellation method that is performed according tothe present invention.

FIG. 27 is an operational flow diagram illustrating another embodimentof an interference cancellation method that is performed according tothe present invention.

FIG. 28 is a diagram illustrating an embodiment of a spectrum ofnarrowband interference that may be addressed and overcome whenpracticing via the present invention.

FIG. 29 is a diagram illustrating an embodiment of a spectrum of adaptedcode showing null at a location of interference that may be achievedwhen practicing via the present invention.

FIG. 30A is a diagram illustrating an embodiment of a receivedconstellation before interference has been cancelled when practicing viathe present invention.

FIG. 30B is a diagram illustrating an embodiment of a receivedconstellation after interference has been cancelled when practicing viathe present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides a solution for interference cancellationfor communication systems (where a medium is used by one user or ifshared among many users). More specifically, the present invention isapplicable within code-division multiple access (CDMA) communicationsystems, as well as synchronous code-division multiple access (S-CDMA)communication systems. One particular type of S-CDMA communicationsystem that may benefit from the present invention is the Data OverCable Service Interface Specifications (DOCSIS) version 2.0 S-CDMA thatis operable for communication systems. The present invention presents asolution that provides for cancellation of interference in any suchcommunication systems. The interference cancellation may be viewed asbeing directed primarily towards the type of interference that occupiesa small number of signal dimensions. Examples of such types ofinterference include narrowband interference (herein also referred to asingress) or impulse/burst noise. The present invention also provides asolution where it may operate in the presence of simultaneous narrowbandinterference and impulse/burst noise and to substantially eliminate themboth.

The present invention provides an approach for interference cancellationthat provides a number of benefits including a completely linear methodof canceling ingress that employed no DFE (Decision Feedback Equalizer)or SIC (Successive Ingress Cancellation). This approach can cancelwideband ingress and may be implemented in a relatively simple andefficient structure. Moreover, the present invention may be combinedrelatively easily, given its simple and efficient structure, with othermethods and systems that may assist in the interference cancellation.

The present invention uses a linear combination of the unused dimensions(for example, the unused codes) to cancel the interference. This may bedone after the de-spreader, or, equivalently, as part of thede-spreading process. There is no appreciable inter-code interferenceintroduced and no decision errors are made as part of this process. Theallocation of unused codes reduces the capacity of the system by a smallamount; for example, to 120/128 of the original capacity for a system of128 codes where 8 unused codes are employed.

It is noted here that the specific examples of 120 active codes, and 8unused codes in a system having 128 available codes is exemplary.Clearly, other embodiments may be employed (having different numbers ofcodes—both different numbers of used and unused) without departing fromthe scope and spirit of the invention.

From certain perspectives, the present invention may be viewed as beingan extension of sub-space modulation that is employed for TDMA (TimeDivision Multiple Access), and it may then be extended to S-CDMA(Synchronous Code Division Multiple Access). To begin this discussion,we consider an example case where 120 active codes are used andnarrowband ingress (narrowband interference) is present. The remaining 8codes are then transmitted as true zero symbols. At the receiver, theunused 8 codes are received with samples of the narrowband ingress. Thisinformation may then be used to cancel the ingress in the same mannerthat is used in sub-space modulation. The 8 unused codes are consideredas extra dimensions and the receiver is trained based on thisinformation.

We continue on with 128 code example (8 of the codes being unused). Byemploying the 8 unused spreading codes, linear combinations of these 8codes may be added to any other code that is transmitted from atransmitter to a receiver, and the resulting composite waveform can beused for de-spreading that one transmitted code. Since, ideally, nosignal is present on any of these 8 codes (being zero codes), thenlittle or no inter-code interference from the transmitters will beinduced. In AWGN (Additive White Gaussian Noise), the inclusion of theseadditional de-spreading codes serves to merely increase the noise at thedecision slicer for the code of interest. However, in the presence ofinterference, such as narrowband interference, some combination of thesecodes in the de-spreading process is operable to reduce the ingressenough to overcome the increased AWGN and make it worthwhile.Heuristically, the unused codes may correlate somewhat with theinterference, and if so, may be used to “subtract” some component of theinterference at the decision slicer, as a type of noise canceler.

The similarity of this approach is somewhat analogous to thefunctionality of an ICF (Ingress Cancellation Filter). In certainembodiments, a TDMA-only, CDMA-only, and/or a TDMA/CDMA burst receivermay be leveraged for this S-CDMA application, including the use of theTrench method or derivative that is mentioned below.

It is noted that the approach to reducing the interference power at thedecision point using only the unused codes may not be optimal in certainembodiments, since using codes with data carried on them may offer someinterference rejection overcoming the introduction of the transmitterinter-code interference. It is also noted that including “in use” codeswould actually provide benefit in practical situations.

It is also noted that using a strict LMS (Least Mean Square) type ofapproach to converging 128 taps to the desired de-spreading code mayprove laborious (in terms of requiring many iterations). This approachdoes not focus on just the unused codes, and has far more degrees offreedom than just finding 8 coefficients for the weightings of the 8unused codes.

Analysis has shown that indeed there is great similarity in theformulation and solution of the optimal taps in the monic filter of theICF for ingress cancellation, and in this application of unusedspreading codes in ingress cancellation for S-CDMA. Both can beformulated in a LS (Least Squares) type of problem, with the ensuingtypical solution taking form.

One advantage that may arise for the TDMA ICF case is when the matrix tobe inverted is Toeplitz (a Toeplitz matrix is a matrix in which all theelements are the same along any diagonal that slopes from northwest tosoutheast), and thus admits significant computational advantages, suchas discovered by William Trench.

However, in the S-CDMA formulation with unused codes, the matrix to beinverted is not Toeplitz, and the Trench approach does not apply. Therestill may be some computational advantages due to the underlyingconstruction of the matrix to be inverted, but it may be that only thetraditional numerical methods such as Cholesky decomposition mayintroduce simplification. The matrix to be inverted is at least of theform C*RC, where C=128×8, with each column orthogonal with the others (asub-matrix of a Unitary matrix), and R=128×128 and is Toeplitz, and *stands for complex conjugate.

One implementation of the present invention may be described as shownbelow.

Let R=R_(m,n)=E{r*(m) r(n)}, where r(n) are noise and ingress samples,containing little or no signal. R is 128×128, where the samplescorrespond to the noise in the chips of a spreading interval. Thesymbol * denotes complex conjugate. This is the noise (or noise plusinterference) covariance matrix.

Let C=[c1 c2 c3 c4 c5 c6 c7 c8], where ci=column of 128 chips of i^(th)unused spreading code. C is 128 rows by 8 columns.

Let:

dsc_(opt)=optimal de-spreading code for code-of-interest c_(k), (writtenalternatively below)dsc _(opt) =C _(k) +w ₁ c1+w ₂ c2+ . . . +w ₈ c8,

where dsc_(opt) is a column vector with 128 components, and w₁, arescalar weighting coefficients.

Thus, dsc_(opt)=[1 w₁ w₂ . . . w₈][C_(k) c1 c2 . . . c8], and we can seethat the optimal solution for the S-CDMA case indeed has a form similarto the monic filter in the TDMA ICF solution.

Let w_(opt)=[w₁ w₂ . . . w₈] which provides the optimal de-spreading forsignaling with the k^(th) spreading code.

It can be shown that w_(opt)=−[C^(T)RC]⁻¹[C^(T)R]c_(k), where all thevectors, matrices, and notation are as defined above.

It is noted that with the ICF in TDMA,w _(opt) =−[R] ⁻¹ [r1 r2 r3 . . . r16]^(T), where

$R = \left\lbrack \begin{matrix}{r0} & {r1} & {r2} & \cdots & {r16} \\{{r1}*} & {r0} & {r1} & \cdots & {r15} \\\vdots & \; & \; & ⋰ & \vdots \\{{r16}*} & {{r15}*} & \cdots & {{r1}*} & {r0}\end{matrix} \right\rbrack$

Another characteristic of the present invention is that the complexityof the method with the LS approach is high for large matrices comparedto the ICF and Trench method with TDMA. However, this complexity ismitigated by the reduced matrix size resulting from the sub-spaceprojection approach described here and below. From certain perspectives,the S-CDMA approach with unused codes may be viewed as not lendingitself to the computational efficiencies of Trench approach or itsderivatives.

However, using an LMS tap update approach has been found to work. Theweights of the unused spreading codes, wi, are updated in LMS fashion.In this method, the de-spreader for the code of interest is input to adecision slicer. The resulting complex error is computed. Similarly,each unused spreading code has its corresponding de-spreading operating.The result of the de-spreader corresponding to an unused spreading codeis “signal,” just as the “signal” rests in the various shift registersin the conventional FIR (Finite Impulse Response) filter in the normalLMS. The de-spread outputs for each of the unused codes is multiplied bythe error vector, and then multiplied by a step size factor “-mu” andadded to the existing tap weight, to update the tap weight.

With 8 unused spreading codes, there is a set of 8 tap weights for eachused spreading code. Thus, with the 8 unused spreading codes, there are8×120 tap weights to iterate.

The LMS approach is much simpler and less computationally intensive thanan LS approach. Also, adapting in the case of S-CDMA weights of a smallnumber of unused codes (an example being 8 unused codes) requires muchless computation than adjusting all coefficients (an example being 128total coefficients) of individual de-spreading operations. This approachis beneficial for a number of reasons. It is computationally acceptable,in that, it limits the number of taps to only 8 (in our continuingexample of 8 unused spreading codes), which almost certainly providesmuch more rapid convergence and less “tap noise.” In addition, iteliminates from the search for optimal coefficients in the de-spreaderthose codes that are known to correspond to used codes.

FIG. 1 is a system diagram illustrating an embodiment of a CMcommunication system 100 that is built according to the presentinvention. The CM communication system includes a number of CMs (shownas a CM user #1 111, a CM user #2 115, . . . , and a CM user #n 121) anda CMTS 130. The CMTS 130 is a component that exchanges digital signalswith CMs on a cable network.

Each of a number of CM users, shown as the CM user #1 111, the CM user#2 115, . . . , and the CM user #n 121, is able to communicativelycouple to a CM network segment 199. A number of elements may be includedwithin the CM network segment 199. For example, routers, splitters,couplers, relays, and amplifiers may be contained within the CM networksegment 199 without departing from the scope and spirit of theinvention.

The CM network segment 199 allows communicative coupling between a CMuser and a cable headend transmitter 120 and/or a CMTS 130. In someembodiments, a cable CMTS is in fact contained within a headendtransmitter. In other embodiments, the functionality of the cable CMTSand the headend transmitter are represented as two distinct functionalblocks so that their respective contribution may be more easilyappreciated and understood. This viewpoint is shown in the situationwhere the CMTS 130 is pictorially shown as being located externally to acable headend transmitter 120. In the more common representation andimplementation, a CMTS 135 is located within the cable headendtransmitter 120. The combination of a CMTS and a cable headendtransmitter may be referred to as being the “cable headend transmitter;”it then being understood that the cable headend transmitter supports theCMTS functionality. The CMTS 130 may be located at a local office of acable television company or at another location within a CMcommunication system. In the following description, the CMTS 130 is usedfor illustration; yet, the same functionality and capability asdescribed for the CMTS 130 may equally apply to embodiments thatalternatively employ the CMTS 135. The cable headend transmitter 120 isable to provide a number of services including those of audio, video,telephony, local access channels, as well as any other service known inthe art of cable systems. Each of these services may be provided to theone or more CM users 111, 115, . . . , and 121.

In addition, through the CMTS 130, the CM users 111, 115, . . . , 121are able to transmit and receive data from the Internet, . . . , and/orany other network to which the CMTS 130 is communicatively coupled. Theoperation of a CMTS, at the cable-provider's head-end, may be viewed asproviding many of the same functions provided by a digital subscriberline access multiplexor (DSLAM) within a digital subscriber line (DSL)system. The CMTS 130 takes the traffic coming in from a group ofcustomers on a single channel and routes it to an Internet ServiceProvider (ISP) for connection to the Internet, as shown via the Internetaccess. At the head-end, the cable providers will have, or lease spacefor a third-party ISP to have, servers for accounting and logging,dynamic host configuration protocol (DHCP) for assigning andadministering the Internet protocol (IP) addresses of all the cablesystem's users, and typically control servers for a protocol called DataOver Cable Service Interface Specifications (DOCSIS), the major standardused by U.S. cable systems in providing Internet access to users.

The downstream information flows to all of the connected CM users 111,115, . . . , 121; this may be viewed to be in a manner that is similarto that manner within an Ethernet network. The individual networkconnection, within the CM network segment 199, decides whether aparticular block of data is intended for it or not. On the upstreamside, information is sent from the CM users 111, 115, . . . , 121 to theCMTS 130; on this upstream transmission, the users within the CM users111, 115, . . . , 121 to whom the data is not intended do not see thatdata at all. As an example of the capabilities provided by a CMTS, theCMTS will enable as many as 1,000 users to connect to the Internetthrough a single 6 MHz channel. Since a single channel is capable of30–40 megabits per second of total throughput, this means that users maysee far better performance than is available with standard dial-upmodems. Embodiments implementing the present invention are describedbelow and in the various Figures that show the data handling and controlwithin one or both of a CM and a CMTS within a CM system that operatesby employing S-CDMA (Synchronous Code Division Multiple Access).

The CMs of the CM users 111, 115, . . . , 121 and the CMTS 130communicate synchronization information to one another to ensure properalignment of transmission from the CM users 111, 115, . . . , 121 to theCMTS 130. This is where the synchronization of the S-CDMA communicationsystems is extremely important. When a number of the CMs all transmittheir signals at a same time such that these signals are received at theCMTS 130 on the same frequency and at the same time, they must all beable to be properly de-spread and decoded for proper signal processing.

Each of the CMs users 111, 115, . . . , 121 is located a respectivetransmit distance from the CMTS 130. In order to achieve optimumspreading diversity and orthogonality for the CMs users 111, 115, . . ., 121 to transmission of the CMTS 130, each of the CM transmissions mustbe synchronized so that it arrives, from the perspective of the CMTS130, synchronous with other CM transmissions. In order to achieve thisgoal, for a particular transmission cycle, each of the CMs 111, 115, . .. , 121 will typically transmit to the CMTS 130 at a respectivetransmission time, which will likely differ from the transmission timesof other CMs. These differing transmission times will be based upon therelative transmission distance between the CM and the CMTS 130. Theseoperations may be supported by the determination of the round tripdelays (RTPs) between the CMTS 130 and each supported CM. With theseRTPs determined, the CMs may then determine at what point to transmittheir S-CDMA data so that all CM transmissions will arrive synchronouslyat the CMTS 130.

The present invention enables interference cancellation within the CMTS130, as shown in a functional block 131. The present invention may alsobe implemented to support interference cancellation within any one ofthe CMs 111, 115, . . . , 121; the particular implementation ofinterference cancellation is shown as a functional block 122 within theCM 122, yet it is understood that the interference cancellationfunctionality may also be supported within the other CMs as well. TheCMTS 130 receives an input spread signal and is operable to performdispreading and interference cancellation according to the presentinvention. The CMTS 130 is operable to employ a linear combiner, thatuses as inputs complex valued combining weights to the particular codesthat are selectively used to assist in the interference cancellation ofone of the de-spread signals that is de-spread from the input spreadsignal that the CMTS 130 receives. Alternatively, the present inventionmay be viewed as employing at least one of an adapted code and anadapted code matrix to perform interference cancellation according tothe present invention.

FIG. 2 is a system diagram illustrating another embodiment of a CMcommunication system 200 that is built according to the presentinvention. From certain perspectives, the FIG. 2 may be viewed as acommunication system allowing bi-directional communication between acustomer premise equipment (CPE) 240 and a network. In some embodiments,the CPE 240 is a personal computer or some other device allowing a userto access an external network. The network may be a wide area network(WAN) 280, or alternatively, the Internet 290 itself. For example, theCM communication system 200 is operable to allow Internet protocol (IP)traffic to achieve transparent bi-directional transfer between aCMTS-network side interface (CMTS-NSI: viewed as being between the CMTS230 and the Internet 290) and a CM to CPE interface (CMCI: viewed asbeing between the CM 210 and the CPE 240).

The WAN 280, and/or the Internet 290, is/are communicatively coupled tothe CMTS 230 via a CMTS-NSI. The CMTS 230 is operable to support theexternal network termination, for one or both of the WAN 280 and theInternet 290. The CMTS 230 includes a modulator and a demodulator tosupport transmitter and receiver functionality to and from a CM networksegment 299. The receiver functionality within the CMTS 230 is operableto support interference cancellation functionality 231 according to thepresent invention. It is also noted that there may be embodiment wherethe CM 210 is also operable to support interference cancellationfunctionality using the present invention, as shown by a functionalblock 211. Implementing interference cancellation in the transmitterprevents noise enhancement that occurs when interference cancellation isperformed in the receiver.

A number of elements may be included within the CM network segment 299.For example, routers, splitters, couplers, relays, and amplifiers may becontained within the CM network segment 299 without departing from thescope and spirit of the invention. The CM network segment 299 allowscommunicative coupling between a CM user and the CMTS 230. The FIG. 2shows just one of many embodiments where the interference cancellation,performed according to the present invention, may be performed toprovide for improved operation within a communication system.

FIG. 3A is a system diagram illustrating an embodiment of a cellularcommunication system 300A that is built according to the presentinvention. A mobile transmitter 310 has a local antenna 311. The mobiletransmitter 310 may be any number of types of transmitters including acellular telephone, a wireless pager unit, a mobile computer havingtransmit functionality, or any other type of mobile transmitter. Themobile transmitter 310 transmits a signal, using its local antenna 311,to a base station receiver 340 via a wireless communication channel. Thebase station receiver 340 is communicatively coupled to a receivingwireless tower 349 to be able to receive transmission from the localantenna 311 of the mobile transmitter 310 that have been communicatedvia the wireless communication channel. The receiving wireless tower 349communicatively couples the received signal to the base station receiver340.

The base station receiver 340 is then able to support interferencecancellation functionality according to the present invention, as shownin a functional block 341, on the received signal. The FIG. 3A shows yetanother of the many embodiments where the interference cancellation,performed according to the present invention, may be performed toprovide for improved operation within a communication system.

FIG. 3B is a system diagram illustrating another embodiment of acellular communication system that is built according to the presentinvention. From certain perspectives, the FIG. 3B may be viewed as beingthe reverse transmission operation of the cellular communication system300B of the FIG. 3A. A base station transmitter 320 is communicativelycoupled to a transmitting wireless tower 321. The base stationtransmitter 320, using its transmitting wireless tower 321, transmits asignal to a local antenna 339 via a wireless communication channel. Thelocal antenna 339 is communicatively coupled to a mobile receiver 330 sothat the mobile receiver 330 is able to receive transmission from thetransmitting wireless tower 321 of the base station transmitter 320 thathave been communicated via the wireless communication channel. The localantenna 339 communicatively couples the received signal to the mobilereceiver 330. It is noted that the mobile receiver 330 may be any numberof types of transmitters including a cellular telephone, a wirelesspager unit, a mobile computer having transmit functionality; or anyother type of mobile transmitter.

The mobile receiver 330 is then able to support interferencecancellation functionality according to the present invention, as shownin a functional block 331, on the received signal. The FIG. 3B shows yetanother of the many embodiments where the interference cancellationfunctionality, performed according to the present invention, may beperformed to provide for improved operation within a communicationsystem.

It is also noted that the embodiments described above within the FIGS.3A and 3B may operate in conjunction within a single communicationsystem. That is to say, a mobile unit (that supports both transmit andreceive functionality) may be implemented to support interferencecancellation functionality during receipt of signals while the basestation device (that supports both transmit and receive functionality)may also be implemented to support interference cancellationfunctionality during receipt of signals. This way, both devices areoperable to support the interference cancellation functionalityaccording to the present invention at both ends of the communicationlink. This dual-end interference cancellation functionality is also truewithin other of the various embodiments described herein that illustrateboth ends of a communication link.

It is further noted that the embodiments described above within theFIGS. 3A and 3B1 may operate in conjunction within a singlecommunication system from yet another perspective. A mobile transmittermay be implemented to support interference cancellation functionalityduring signal processing and transmission of its signals to a basestation receiver. Similarly, a base station transmitter may beimplemented to support interference cancellation functionality duringsignal processing and transmission of its signals to a mobile unitreceiver. This may be performed, at least in part, by adjusting atransmitted spectrum to meet a desired spectral mask. It may bedesirable to attenuate certain portions of the spectrum using thesubspace canceler. In these applications the canceler is predominantlylocated in the transmitter. Further detail of this interferencecancellation within a transmitter device is presented below. Thisadjusting of a transmitted spectrum to meet a desired spectral mask maybe performed within any of the various embodiments that include atransmitter that transmits a signal to a receiver according to thepresent invention.

FIG. 4 is a system diagram illustrating an embodiment of a satellitecommunication system 400 that is built according to the presentinvention. A transmitter 420 is communicatively coupled to a wirednetwork 410. The wired network 410 may include any number of networksincluding the Internet, proprietary networks, and other wired networks.The transmitter 420 includes a satellite earth station 451 that is ableto communicate to a satellite 453 via a wireless communication channel.The satellite 453 is able to communicate with a receiver 430. Thereceiver 430 is also located on the earth. Here, the communication toand from the satellite 453 may cooperatively be viewed as being awireless communication channel, or each of the communication to and fromthe satellite 453 may be viewed as being two distinct wirelesscommunication channels.

For example, the wireless communication “channel” may be viewed as notincluding multiple wireless hops in one embodiment. In otherembodiments, the satellite 453 receives a signal received from thesatellite earth station 451, amplifies it, and relays it to the receiver430; the receiver 430 may include terrestrial receivers such assatellite receivers, satellite based telephones, and satellite basedInternet receivers, among other receiver types. In the case where thesatellite 453 receives a signal received from the satellite earthstation 451, amplifies it, and relays it, the satellite 453 may beviewed as being a “transponder.” In addition, other satellites may existthat perform both receiver and transmitter operations. In this case,each leg of an up-down transmission via the wireless communicationchannel would be considered separately. The wireless communicationchannel between the satellite 453 and a fixed earth station would likelybe less time-varying than the wireless communication channel between thesatellite 453 and a mobile station.

In whichever embodiment, the satellite 453 communicates with thereceiver 430. The receiver 430 may be viewed as being a mobile unit incertain embodiments (employing a local antenna 412); alternatively, thereceiver 430 may be viewed as being a satellite earth station 452 thatmay be communicatively coupled to a wired network in a similar mannerthat the satellite earth station 451, within the transmitter 420,communicatively couples to a wired network. In both situations, thereceiver 430 is able to support interference cancellation functionality,as shown in a functional block 431, according to the present invention.For example, the receiver 430 is able to perform interferencecancellation, as shown in a functional block 431, on the signal receivedfrom the satellite 453. The FIG. 4 shows yet another of the manyembodiments where the interference cancellation, performed according tothe present invention, may be performed to provide for improved receiverperformance.

FIG. 5A is a system diagram illustrating an embodiment of a microwavecommunication system 500A that is built according to the presentinvention. A tower transmitter 511 includes a wireless tower 515. Thetower transmitter 511, using its wireless tower 515, transmits a signalto a tower receiver 512 via a wireless communication channel. The towerreceiver 512 includes a wireless tower 516. The wireless tower 516 isable to receive transmissions from the wireless tower 515 that have beencommunicated via the wireless communication channel. The tower receiver512 is then able to support interference cancellation functionality, asshown in a functional block 533. The FIG. 5A shows yet another of themany embodiments where interference cancellation, performed according tothe present invention, may be performed to provide for improved receiverperformance.

FIG. 5B is a system diagram illustrating an embodiment of apoint-to-point radio communication system 500B that is built accordingto the present invention. A mobile unit 551 includes a local antenna555. The mobile unit 551, using its local antenna 555, transmits asignal to a local antenna 556 via a wireless communication channel. Thelocal antenna 556 is included within a mobile unit 552. The mobile unit552 is able to receive transmissions from the mobile unit 551 that havebeen communicated via the wireless communication channel. The mobileunit 552 is then able to support interference cancellationfunctionality, as shown in a functional block 553, on the receivedsignal. The FIG. 5B shows just yet another of the many embodiments whereinterference cancellation, performed according to the present invention,may be performed to provide for improved receiver performance.

FIG. 6 is a system diagram illustrating an embodiment of a highdefinition (HDTV) communication system 600 that is built according tothe present invention. An HDTV transmitter 610 includes a wireless tower611. The HDTV transmitter 610, using its wireless tower 611, transmits asignal to an HDTV set top box receiver 620 via a wireless communicationchannel. The HDTV set top box receiver 620 includes the functionality toreceive the wireless transmitted signal. The HDTV set top box receiver620 is also communicatively coupled to an HDTV display 630 that is ableto display the demodulated and decoded wireless transmitted signalsreceived by the HDTV set top box receiver 620.

The HDTV set top box receiver 620 is then able to support interferencecancellation functionality, as shown in a functional block 623 toprovide for improved receiver performance. The FIG. 6 shows yet anotherof the many embodiments where interference cancellation, performedaccording to the present invention, may be performed to provide forimproved receiver performance.

FIG. 7 is a system diagram illustrating an embodiment of a communicationsystem that is built according to the present invention. The FIG. 7shows communicative coupling, via a communication channel 799, betweentwo transceivers, namely, a transceiver 701 and a transceiver 702. Thecommunication channel 799 may be a wireline communication channel or awireless communication channel.

Each of the transceivers 701 and 702 includes a transmitter and areceiver. For example, the transceiver 701 includes a transmitter 749and a receiver 740; the transceiver 702 includes a transmitter 759 and areceiver 730. The receivers 740 and 730, within the transceivers 701 and702, respectively, are each operable to support interferencecancellation functionality according to the present invention. This willallow improved signal processing for both of the transceivers 701 and702. For example, the receiver 740, within the transceiver 701, is ableto support interference cancellation functionality, as shown in afunctional block 741, on a signal received from the transmitter 759 ofthe transceiver 702. Similarly, the receiver 730, within the transceiver702, is able to support interference cancellation functionality, asshown in a functional block 731, on a signal received from thetransmitter 749 of the transceiver 701.

If desired in certain embodiments, the transmitters 749 and 759, withinthe transceivers 701 and 702, respectively, are each operable to supportinterference cancellation functionality according to the presentinvention. This will also allow improved signal processing for both ofthe transceivers 701 and 702. For example, the transmitter 749, withinthe transceiver 701, is able to support interference cancellationfunctionality, as shown in a functional block 748, on a signal that isto be transmitted from the transmitter 759 of the transceiver 702.Similarly, the transmitter 759, within the transceiver 702, is able tosupport interference cancellation functionality, as shown in afunctional block 758, on a signal that is to be transmitted from thetransmitter 759 of the transceiver 702.

This interference cancellation functionality, within the transmitters749 and 759, respectively, may be performed, at least in part, byadjusting a transmitted spectrum to meet a desired spectral maskaccording to the present invention. The FIG. 7 shows yet another of themany embodiments where interference cancellation, performed according tothe present invention, may be performed to provide for improvedperformance.

FIG. 8 is a system diagram illustrating another embodiment of acommunication system 800 that is built according to the presentinvention. The FIG. 8 shows communicative coupling, via a communicationchannel 899, between a transmitter 849 and a receiver 830. Thecommunication channel 899 may be a wireline communication channel or awireless communication channel. The receiver 830 is operable to supportinterference cancellation, as shown in a functional block 831, accordingto the present invention. The FIG. 8 shows yet another of the manyembodiments where interference cancellation, performed according to thepresent invention, may be performed to provide for improved performance.

In certain embodiments, the transmitter 849 is also operable to supportinterference cancellation, as shown in a functional block 848, accordingto the present invention. This interference cancellation functionality,within the transmitter 849, may be performed, at least in part, byadjusting a transmitted spectrum to meet a desired spectral maskaccording to the present invention. For example, the interferencecancellation functionality of the present invention may be located atthe transmitter 849, the receiver 830, or partly in each (as shown bythe functional blocks 848 and 831). In many of the various embodimentsdescribed herein, the interference cancellation functionality has beenlocated in a receiver of a communication system. The following describesone embodiment of how the interference cancellation functionality may belocated at the transmitter. The unused codes, instead of being modulatedat the transmitter with zero symbols, are modulated with a linearcombination of the desired signals from the used codes. In the case ofnarrowband interference, the resulting transmitted signal will have anull on the interferer.

FIG. 9 is a system diagram illustrating an embodiment of a CMTS system900 that is built according to the present invention. The CMTS system900 includes a CMTS medium access controller (MAC) 930 that operateswith a number of other devices to perform communication from one or moreCMs to a WAN 980. The CMTS MAC 930 may be viewed as providing thehardware support for MAC-layer per-packet functions includingfragmentation, concatenation, and payload header suppression that allare able to offload the processing required by a system centralprocessing unit (CPU) 972. This will provide for higher overall systemperformance. In addition, the CMTS MAC 930 is able to provide supportfor carrier class redundancy via timestamp synchronization across anumber of receivers, shown as a receiver 911, a receiver 911, and areceiver 913 that are each operable to receive upstream analog inputs.In certain embodiments, each of the receivers 911, 912, and 913 are dualuniversal advanced TDMA/CDMA (Time Division Multiple Access/CodeDivision Multiple Access) PHY-layer burst receivers. That is top say,each of the receivers 911, 912, and 913 includes at least one TDMAreceive channel and at least one CDMA receive channel; in this case,each of the receivers 911, 912, and 913 may be viewed as beingmulti-channel receivers.

In addition, the CMTS MAC 930 may be operated remotely with arouting/classification engine 979 that is located externally to the CMTSMAC 930 for distributed CMTS applications including mini fiber nodeapplications. Moreover, a Standard Programming Interface (SPI) masterport may be employed to control the interface to the receivers 911, 912,and 913 as well as to a downstream modulator 920.

The CMTS MAC 930 may be viewed as being a highly integrated CMTS MACintegrated circuit (IC) for use within the various DOCSIS and advancedTDMA/CDMA physical layer (PHY-layer) CMTS products. The CMTS MAC 930 mayemploy hardware engines for upstream and downstream paths. The upstreamprocessor design is segmented and uses two banks of Synchronous DynamicRandom Access Memory (SDRAM) to minimize latency on internal buses. Thetwo banks of SDRAM used by the upstream processor are shown as upstreamSDRAM 975 (operable to support keys and reassembly) and SDRAM 976(operable to support Packaging, Handling, and Storage (PHS) and outputqueues). The upstream processor performs Data Encryption Standard (DES)decryption, fragment reassembly, de-concatenation, payload packetexpansion, packet acceleration, upstream Management Information Base(MIB) statistic gathering, and priority queuing for the resultantpackets. Each output queue can be independently configured to outputpackets to either a Personal Computer Interface (PCI) or a Gigabit MediaIndependent Interface (GMII). DOCSIS MAC management messages andbandwidth requests are extracted and queued separately from data packetsso that they are readily available to the system controller.

The downstream processor accepts packets from priority queues andperforms payload header suppression, DOCSIS header creation, DESencryption, Cyclic Redundancy Check (CRC) and Header Check Sequence (ofthe DOCSIS specification), Moving Pictures Experts Group (MPEG)encapsulation and multiplexing, and timestamp generation on the in-banddata. The CMTS MAC 930 includes an out-of-band generator and TDMAPHY-layer (and/or CDMA PHY-layer) interface so that it may communicatewith a CM device's out-of-band receiver for control of power managementfunctions. The downstream processor will also use SDRAM 977 (operable tosupport PHS and output queues). The CMTS MAC 930 may be configured andmanaged externally via a PCI interface and a PCI bus 971.

Each of the receivers 911, 912, and 913 is operable to supportinterference cancellation functionality. For example, the receiver 911is operable to support interference cancellation functionality, as shownin a functional block 991; the receiver 912 is operable to supportinterference cancellation functionality, as shown in a functional block992; and the receiver 913 is operable to support interferencecancellation functionality, as shown in a functional block 993. The FIG.9 shows yet another embodiment in which interference cancellation may beperformed according to the present invention. Any of the functionalityand operations described in the other embodiments may be performedwithin the context of the CMTS system 900 without departing from thescope and spirit of the invention.

FIG. 10 is a system diagram illustrating an embodiment of a burstreceiver system 1000 that is built according to the present invention.The burst receiver system 1000 includes at least one multi-channelreceiver 1010. The multi-channel receiver 1010 is operable to receive anumber of upstream analog inputs that are transmitted from CMs. Theupstream analog inputs may be in the form of either TDMA (Time DivisionMultiple Access) and/or CDMA (Code Division Multiple Access) format. Anumber of receive channels may be included within the multi-channelreceiver 1010.

For example, the multi-channel receiver 1010 is operable to support anumber of TDMA receive channels 1020 (shown as TDMA signal 1 and TDMAsignal 2) and to support interference cancellation functionality, asshown in a functional block 1021, for those received TDMA signals. Themulti-channel receiver 1010 is operable to support a number of TDMAreceive channels 1030 (shown as CDMA signal 1 and CDMA signal 2) and tosupport interference cancellation functionality, as shown in afunctional block 1031, for those received CDMA signals. Genericallyspeaking, the multi-channel receiver 1010 is operable to support anumber of receive channels 1040 (shown as received signal 1 and receivedsignal 2) and to support interference cancellation functionality, asshown in a functional block 1041, for those received signals. Themulti-channel receiver 1010 of the FIG. 10 is operable to interface witha CMTS MAC. The burst receiver system 1000 may include a number ofmulti-channel receivers that are each operable to interface with theCMTS MAC.

In certain embodiments, the multi-channel receiver 1010 provides anumber of various functionalities. The multi-channel receiver 1010 maybe a universal headend advanced TDMA PHY-layer QPSK/QAM (QuadraturePhase Shift Keying/Quadrature Amplitude Modulation) burst receiver; themulti-channel receiver 1010 also include functionality to be a universalheadend advanced CDMA PHY-layer QPSK/QAM burst receiver; or themulti-channel receiver 1010 also include functionality to be a universalheadend advanced TDMA/CDMA PHY-layer QPSK/QAM burst receiver offeringboth TDMA/CDMA functionality. The multi-channel receiver 1010 may beDOCSIS/EuroDOCSIS based, IEEE 802.14 compliant. The multi-channelreceiver 1010 may be adaptable to numerous programmable demodulationincluding BPSK (Binary Phase Shift Keying), and/or QPSK,8/16/32/64/128/256/516/1024 QAM. The multi-channel receiver 1010 isadaptable to support variable symbols rates as well. Other functionalitymay likewise be included to the multi-channel receiver 1010 withoutdeparting from the scope and spirit of the invention. Such variationsand modifications may be made to the communication receiver.

FIG. 11 is a system diagram illustrating an embodiment of a single chipDOCSIS/EuroDOCSIS CM system 1100 that is built according to the presentinvention. The single chip DOCSIS/EuroDOCSIS CM system 1100 includes asingle chip DOCSIS/EuroDOCSIS CM 1110 that is implemented in a very highlevel of integration and offering a very high level of performance. Acoaxial cable in input to a DiPlexer to provide CM access to the singlechip DOCSIS/EuroDOCSIS CM system 600. The DiPlexer communicativelycouples to a CMOS (Complementary Metal Oxide Semiconductor) tuner. TheCMOS tuner may be implemented with a companion part that includes a lownoise amplifier (LNA) and performs radio frequency (RF) automatic gaincontrol (AGC). This two part solution is operable to support 64 and 256QAM. These two parts operate cooperatively with the single chipDOCSIS/EuroDOCSIS CM 1110. The CMOS tuner may be operable to support anintermediate frequency (IF) output frequency range of 36–44 MHz, andspecifically support the 36.125 and 43.75 MHz center frequencies for thePhase Alteration Line (PAL) and National Television System Committee(NTSC) standards. Also, the CMOS tuner and the LNA and RF AGC are DOCSISand EuroDOCSIS standard supportable.

However, it is also noted that the CMOS tuner is operable to performdirect RF to baseband (BB) frequency transformation without requiringthe IF transformation. The received signal from the DiPlexer. Anexternal bandpass Surface Acoustic Wave (SAW) filter removes thechannels distant from the desired signal.

The output from the SAW filter is then passed to the single chipDOCSIS/EuroDOCSIS CM 1110. The single chip DOCSIS/EuroDOCSIS CM 1110 issupported by Synchronous Dynamic Random Access Memory (SDRAM) and Flash.In addition, the single chip DOCSIS/EuroDOCSIS CM 1110 supports bothEthernet and USB interfacing to any other devices that may exist withinthe single chip DOCSIS/EuroDOCSIS CM system 1100. The FIG. 11 shows yetanother embodiment in which interference cancellation may be performedaccording to the present invention. The interference cancellationfunctionality may be supported directly within the single chipDOCSIS/EuroDOCSIS CM 1110. The single chip DOCSIS/EuroDOCSIS CM system1100 shows an application context of yet another implementation of adevice that may perform the present invention.

FIG. 12 is a system diagram illustrating another embodiment of a singlechip DOCSIS/EuroDOCSIS CM system 1200 that is built according to thepresent invention. The single chip DOCSIS/EuroDOCSIS CM system 1200includes a single chip DOCSIS/EuroDOCSIS CM 1210 that combines an RFreceiver with an advanced QAM demodulator, an advanced QAM and S-CDMAmodulator/transmitter, a complete DOCSIS 2.0 Media Access Controller(MAC), a 200 MHz MIPS32 Communication Processor, a 16 bit, 100 MHz SDRAMinterface, 10/100 Ethernet MAC with integrated transceiver and MediaIndependent Interface (MII), and a USB 1.1 controller with integratedtransceiver.

The QAM receiver directly samples a tuner output (such as the CMOS tunerof the FIG. 6) with an 11 bit analog to digital converter (ADC) andinput AGC amplifier. The receiver digitally re-samples and demodulatesthe signal with recovered clock and carrier timing, filters andequalizes the data, and passes soft decisions to an ITU-T J.83 AnnexA/B/C compatible decoder. The receiver supports variable symbol rate4/16/32/64/128/256/1024 QAM Forward Error Correction (FEC) decoding. Thefinal received data stream is delivered in a serial MPEG-2 transportformat. All gain, clock, and carrier, acquisition and tracking loops areintegrated in the QAM receiver.

The upstream transmitter takes burst or continuous data, provides FECencoding and pre-equalization for DOCSIS applications, filters andapplies 2/4/8/16/64/256 QAM or S-CDMA modulation to the data stream,amplifies the signal through the integrated upstream power amplifier andprovides a direct 0–65 MHz analog output.

The MAC of the single chip DOCSIS/EuroDOCSIS CM 1210 includes allfeatures required for full DOCSIS 1.0, 1.1, and 2.0 compliance,including full support for baseline privacy (BPI+) encryption anddecryption. Single-user support includes four SIDS (StandardInteroperable Datalink System) in downstream, four DA perfect matchfilters, a 256 entry CAM for multicast/unicast hash filter and fourindependent upstream queues for simultaneous support of Quality ofService (QoS) and BE traffic. To enhance operational support, the MAC ofthe MAC of the single chip DOCSIS/EuroDOCSIS CM 1210 provides extendedNetwork Management MIB/Diagnostic features, as well as immediate UCC (onthe fly) using independent resets for downstream and upstream queues andboth individual queue reset/flush for upstream queues. The MAC of thesingle chip DOCSIS/EuroDOCSIS CM 1210 uses advance PROPANE™ techniquesto provide packet acceleration to significantly improve upstream channelutilization.

With the incorporation of an upstream power amplifier, the MAC of thesingle chip DOCSIS/EuroDOCSIS CM 1210 allows a complete CM to beassembled with a minimal set of external components. When used with aCMOS tuner, such as the CMOS tuner of the FIG. 11, a very low costsolution for a high performance, single user DOCSIS 2.0 CM is provided.The MAC of the single chip DOCSIS/EuroDOCSIS CM 1210 of the FIG. 12 isoperable to support all digital reference frequency lockingfunctionality according to the present invention. The FIG. 12 shows yetanother embodiment where interference cancellation functionality may besupported according to the present invention. The interferencecancellation functionality may be viewed as being supported andperformed within the DOCSIS 2.0 MAC of the single chip DOCSIS/EuroDOCSISCM 1210 of the FIG. 12.

FIG. 13 is a system diagram illustrating an embodiment of a single chipwireless modem system 1300 that is built according to the presentinvention. The single chip wireless modem system 1300 includes a singlechip wireless modem 1310 that is operable to support a variety offunctionalities. The single chip wireless modem system 1300 is operableto perform wireless LAN operation using an 802.11 radio that is operableto communicatively couple to an external device that is wireless capable(example shown as the pen computer having wireless functionality). Thesingle chip wireless modem 1310 of the single chip wireless modem system1300 employs a 10/100 Ethernet PHY and an HPNA (Home Phoneline NetworkAlliance) analog front end (AFE) that is operable to interface with theHPNA 2.0 network. The single chip wireless modem 1310 of the single chipwireless modem system 1300 also supports capability to communicate withan external device via a USB 1.1 interface.

The single chip wireless modem 1310 of the single chip wireless modemsystem 1300 is compatible with existing cable modem application code. Inaddition, the single chip wireless modem 1310 supports advanced QAMLink®modulation/demodulation TP provide for higher throughputs andperformance in noisy plant environments. The 802.11b MAC and basebandallow for wireless connectivity as mentioned above. In addition, theintegrated HPNA 2.0 MAC supports high-speed multimedia services overphone lines. The integrated 10/100 Ethernet and USB 1.1 with integratedtransceiver provide for a low cost CPE (Customer Premises Equipment),and the MPI interfaces provide for great flexibility through additionalconnectivity options. The single chip wireless modem 1310 is a part of acomprehensive solution that is operable to support certifiableDOCSIS/EuroDOCSIS 1.1 software as well as supporting residential gatewaysoftware including Firewall, NAT and DHCP. The FIG. 13 shows yet anotherembodiment where interference cancellation functionality may besupported according to the present invention. The interferencecancellation functionality may be viewed as being supported andperformed within the single chip wireless modem 1310 of the single chipwireless modem system 1300.

FIG. 14 is a system diagram illustrating another embodiment of a singlechip wireless modem system 1400 that is built according to the presentinvention. The single chip wireless modem system 1400 includes a singlechip wireless modem that is operable to support a variety offunctionalities. The single chip wireless modem of the single chipwireless modem system 1300 integrates the DOCSIS/EuroDOCSIS 2.0 cablebased modem with a 2/416/32/64/128/256/1024 QAM downstream receiver withAnnex A, B, C FEC support. In addition, the single chip wireless modemintegrates the DOCSIS/EuroDOCSIS 2.0 cable based modem with2/4/8/16/32/64/128/256 QAM FA-TDMA ad S-CDMA. The 802.11b wireless MACand baseband are also integrated on the single chip wireless modem. Anumber of other functional blocks are also integrated thereon,including, a 300 MHz MIPS32 CPU, a 32 bit 100 MHz SDRAM/DDR controller,an integrated upstream amplifier, an integrated IP SEC engine, anintegrated advance PROPANE™ packet accelerator, a 12 Mbps USB 1.1 slaveport with integrated transceiver, a 10/100 Ethernet MAC/PHY with MIIinterface, an MPI expansion bus (that supports PCI, Cardbus, and PCMCIAinterfaces), a single 28 MHz reference crystal, and ability to operateusing voltages of 1.8 V and/or 3.3 V.

The advanced QAMLink® technology of the single chip wireless modem,compliant with DOCSIS 2.0, supports up to 1024 QAM downstream modulationformats and both FA-TDMA and S-CDMA, with 256 QAM upstream modulationformats. This advanced technology provides a higher throughput andsuperior performance in noise plant environments, paving the way forsymmetrical services, such as video conferencing.

The single chip wireless modem integrates both wireless and wirelinenetworking functions for distributing broadband content throughout thehome. An 802.11b solution is provided for wireless connectivity, whileboth 10/100 Ethernet and 32 Mbps HPNA 2.0 solutions provide wiredconnectivity. HPNA 2.0 allows multimedia services to be streamed acrossexisting home phone lines.

The PROPANE™ technology provides bandwidth and performance enhancementsto existing cable plants allowing up to twice as many subscribers pernode, thereby minimizing the need for node splits. The FIG. 14 shows yetanother embodiment where interference cancellation functionality may besupported according to the present invention. The interferencecancellation functionality may be viewed as being supported andperformed within the single chip wireless modem of the single chipwireless modem system 1400.

FIG. 15 is a diagram illustrating an embodiment of a vector de-spreader1500 that is built according to the present invention. The followingdescription of embodiments of the present invention using the FIGS. 15,16, 17, and 18 are made within the context of the DOCSIS 2.0 system.This system uses S-CDMA modulation for the upstream with 128 orthogonalcodes. In the example there are 120 active (data-carrying) codes, with 8unused codes. This example is for illustrative purposes only, and shouldby no means limit the scope of the invention. Again, it is noted thatthe specific examples of 120 active codes, and 8 unused codes in asystem having 128 available codes is exemplary. Clearly, otherembodiments may be employed (having different numbers of codes—bothdifferent numbers of used and unused) without departing from the scopeand spirit of the invention.

The FIG. 15 depicts a vector de-spreader, arranged according to thepresent invention, consisting of 128 individual de-spreaders.De-spreading is the process of multiplying by a given code sequence andsumming (or integrating) over the chips of a spreading sequence in thiscase the length of the code, 128 chips. Each scalar de-spreader performsthe function of de-spreading the received signal (input spread signal tobe de-spread) using a single de-spreading code (c₁, . . . , c₁₂₈). Thereare 128 orthogonal de-spreading codes in the present example.

FIG. 16 is a diagram illustrating an embodiment of an interferencecanceler 1200 that is built according to the present invention. Thespread input signal x, consisting of the sum of multiple spreading codesmodulating multiple data streams, enters the diagram at the left. Theundesired interference n is added to the signal. The signal is appliedto the vector de-spreader, which de-spreads each of the 128 codes. Theupper 8 codes are not used for data transmission and are modulated withnumerically zero-valued symbols instead of data. Clearly, there may beembodiments where other numerically constant-valued symbols may beemployed instead of data as well. Further, the symbol may contain datarepresented as a reduced constellation, such as BPSK or QPSK, on the“unused” codes.

One of the 120 data-carrying codes, code d_(s), is identified forillustration in the FIG. 16. In order to cancel the interference, thede-spreader output d_(s) is processed in a linear combiner, where it issummed with a linear combination of the 8 de-spreader outputs from thezero-modulation codes d₁–d₈. The complex-valued combining weightsapplied to these codes are w₁–w₈, respectively. These weights arecomputed in a weight computation method as shown in the lower right handcorner of the FIG. 16 using the weight computation functionality.

The weight computation functionality may employ a method that utilizesthe input spread signal plus interference, and may utilize some systemoutputs if an iterative method is used. Weight computation methods thathave been found valuable are the LMS (least mean square) method and theLS (least squares) method. The result of the linear combination is theoutput {circumflex over (d)}_(s), which is the data stream d_(s), withthe interference largely removed. Although not shown in the figure, thesame linear combiner structure is applied to the other 119 codes as well(all of the other active codes besides the code d_(s)). In each case,the desired code (one of the 120 “active” or data-carrying codes) isapplied to a linear combiner to cancel the interference from that code.For each data-carrying code, the same 8 zero-modulation codes are summedwith the desired code, but for each active code the weights w₁–w₈ are ingeneral unique.

An alternative viewpoint is to define the adapted code as

${c_{a}(n)} = {{c_{s}(n)} + {\sum\limits_{k = 1}^{N_{u}}\;{w_{k}{c_{k}(n)}}}}$that is, the desired code plus the linear combination of the weightstimes the unused (“inactive”) codes. In this view, the adapted code is amodified code with complex coefficients, which is used instead of thecode c_(s) to de-spread a single desired signal from a single modulatedcode, while simultaneously canceling the interference.

This approach can be extended to matrix notation by defining the adaptedcode matrix asC _(adapted) =C _(used) +WC _(unused)where:

C_(adapted)=adapted code matrix, dimension (N_(c)−N_(u))×128, forexample, 120×128

C_(used)=matrix whose rows are the used codes in the original codematrix, dimension (N_(c)−N_(u))×N_(c), for example, 120×128 W=matrixwhose rows are the adaptive weight vectors for each unused code,dimension (N_(c)−N_(u))×N_(u), for example, 120×8

C_(unused)=matrix whose rows are the unused codes in the original codematrix, dimension N_(u)×N_(c), for example, 8×128

N_(c)=number of total codes=number of chips in each code, for example,128

N_(u)=number of unused codes, for example, 8

In this view, the adapted code matrix is a modified code matrix withcomplex coefficients, which is used instead of the code matrix C tode-spread the desired signals from all used codes, while simultaneouslycanceling the interference on all used codes.

It is noted that that the unused codes may be de-spread as well, andthis side information, though not data-carrying, is of use incharacterizing the interference environment.

It is also noted that the weight computation functionality may beperformed offline, and these pre-computed complex-valued combiningweights, w₁–w₈, may then be stored in memory and/or a look up table(LUT) that may be used to provide the complex-valued combining weights,w₁–w₈. The appropriate set of weights may be selected after analyzingthe interference environment.

FIG. 17 is a diagram illustrating another embodiment of an interferencecanceler 1700 that is built according to the present invention. The FIG.17 may be viewed as being somewhat similar to the interference canceler1600 of the FIG. 16 with some exceptions relating to the specific codesthat are used to perform the linear combination in an effort to performthe interference cancellation according to the present invention.

The FIG. 17 shows an embodiment where all of the codes are included inthe linear combiner. This includes both the used codes and the unusedcodes, instead of only the unused codes. This will be useful if there isinter-code interference (ICI), since in that case the desired signalwill appear on all codes. Conversely, the signals modulated onto allcodes will appear on the desired de-spreader output, and can besubtracted from the desired de-spreader output.

In yet another alternative embodiment, to add to the number of effectiveunused codes, we may use codes bearing preamble symbols in addition tothe codes carrying zero-valued symbols. The preamble symbols are knownand can be subtracted once their amplitude and phase have been measured,for example using a preamble correlator. Thus the preamble-bearing codescan also be used as inputs to the linear combiner in order to bettercancel the interference.

There are some other embodiments that may be employed as well. Forexample, the selection of the inactive codes may be performed asfollows: (1) use codes 0, 1, 2, 3, . . . (adjacent codes, as done inDOCSIS 2.0 spec) in which the codes are adjacent and the lower codesused in the coding and/or (2) spacing the codes maximally apart. Forexample, using DOCSIS 2.0 S-CDMA code set, the 8 unused codes out of 128total codes might be code numbers {15 31 47 63 79 95 111 127} whenseeking to perform the maximally spaced apart embodiment. Moreover, theselection of the unused codes may be performed according to anoptimality criterion. Examples of some potential optimality criteriainclude: (1) select unused codes that have maximal correlation with theinterference, (2) minimize enhancement of white noise resulting fromcancellation process, and (3) minimize residual interference power aftercancellation.

It is also noted that the particular codes that are selected as theunused codes may change over time during the processing of receivedsignals. Moreover, the particular selection of the codes may vary fromone iteration to the next. For example, in one situation, adjacent codesmay be selected as the unused codes. In another situation, the maximallyspaced codes may be selected as the unused codes.

The selection of the codes that are to be designated the unused codesmay be performed using a variety of approaches including: (1) employingcode matrix reordering, (2) employing null grant periods, (2) zeropadding data, and/or (4) employing some optimality criterion (orcriteria).

Similar to the embodiment of the FIG. 16, it is also noted that theweight computation functionality may be performed offline, and thesepre-computed complex-valued combining weights that are used here in theFIG. 17 may similarly be stored in memory and/or a look up table (LUT)that may be used to provide the complex-valued combining weights. Theappropriate set of weights may be selected after analyzing theinterference environment. This may similarly be performed in theembodiments of the FIGS. 18 and 19 described in further detail belowwhere these pre-computed complex-valued combining weights may also bestored in memory and/or a look up table (LUT).

FIG. 18 is a diagram illustrating another embodiment of an interferencecanceler 1800 that is built according to the present invention. The FIG.18 may be viewed as being a variant of the FIG. 17 that has access toany of the codes (including both used and unused codes). The FIG. 18includes a subset of the codes for use in the linear combiner, insteadof all the codes or only the unused codes. For example, in DOCSIS 2.0S-CDMA, adjacent codes are nearly shifts of each other. When a timingoffset occurs, the codes lose orthogonality and ICI occurs. However, theICI is predominant on the adjacent codes. For example, in the presenceof a timing offset, code 35 will be interfered with predominantly bycodes 34 and 36, with lesser effects coming from codes 33 and 37, evenlesser effects from codes 32 and 38, and so on. Hence including asinputs to the linear combiner the data-bearing codes 33, 34, 36 and 37,plus the unused codes, but not the remaining data-bearing codes, willreduce the number of weights that have to be solved for compared to themore general case above in which all codes are included in the linearcombination. Another embodiment would involve including as inputs to thelinear combiner the data-bearing codes 34, and 36, plus the unusedcodes, but not the remaining data-bearing codes, in an effort to try toreduce the number of weights that have to be solved for compared to themore general case above in which all codes are included in the linearcombination.

FIG. 19 is a diagram illustrating an embodiment of an interferencecanceler with memory 1900 that is built according to the presentinvention. The FIG. 19 shows an interference canceler with memory, thatis, it uses the history of previous samples in computing the output. Theweight w₁ has been replaced with “feed-forward equalizer 1” (FF Eqer.1), a tapped delay line or FIR filter with L weights. The other adaptiveweights have similarly been replaced with FF equalizers 2–8. It is notedthat both the current and past soft de-spread symbols are included inthe linear combination. Moreover, future soft de-spread symbols may alsobe included in the linear combination; these future soft de-spreadsymbols are “future” relative to the symbol currently being estimated.This permits each tap to have a frequency selective response.

FIG. 20 is a diagram illustrating an embodiment of equalization withcanceler 2000 that is arranged according to the present invention. TheFIG. 20 may be viewed as being a representation of equalization ofchannel response, and cancellation of resulting colored noise. Thecanceler structure can also be used to help with equalization. The FIG.20 considers a communications system with a transmitter 2010, a channel2020 having a response H(f), and a receiver 2025. Let the channelresponse be H(f). We assume, as an example, that H(f) exhibits a null atsome frequency in the signaling band of interest. Assume AWGN (additivewhite Gaussian noise) is added in the channel after H(f). We may use astandard adaptive equalizer 2030 at the receiver to provide the inverse(zero forcing) response, 1/H(f), which will have a narrow peak at thefrequency location where the null exists in H/(f). This peak will causethe white noise to be colored and to have a peak as well. Thisnarrowband colored noise can be canceled (using the canceler 2040) bythe present technique in exactly the same manner that other narrowbandinterference is canceled. The FIG. 20 shows yet another embodiment ofhow interference cancellation, according to the present invention, maybe performed.

FIG. 21 is a diagram illustrating an embodiment of Least Means Square(LMS) training of an interference canceler 2100 according to the presentinvention. The FIG. 21 may be viewed as being one embodiment that isoperable to perform adaptation of an interference canceler usingiterative methods. The present interference canceler 2100 can be adaptedusing iterative methods such as LMS or RLS. The FIG. 21 illustrates howthe LMS method may be used to adapt the canceler weights. The output ofthe de-spreader for the desired code (containing soft decisions) issliced to produce hard symbol decisions. If known training symbols areavailable, they replace the hard decisions, which may contain symbolerrors, especially upon startup. The difference between the hard (orknown) and soft decisions gives the LMS error sample. The error iscorrelated with the outputs of the unused code de-spreaders and used toupdate the adaptive weights wi.

Within the FIG. 21, the slicer, the MUX, and the LMS error (and LMSstep-size scaling μ) that are used to update the adaptive weights wi maybe viewed as being just one embodiment of an iterative, errordetermining approach. Clearly, other error determining approaches(besides LMS) may be employed without departing from the scope andspirit of the invention. The error calculation and correlation with theoutputs of the unused code de-spreaders that are used to update theadaptive weights wi may be viewed as being an iterative adaptive weightfunctionality that may be viewed as being provided in an implementationvia an iterative adaptive weight functional block that communicativelycouples to each of the outputs of the unused code de-spreaders.

FIG. 22A is a diagram illustrating an embodiment of signaltransformation according to the present invention. The FIG. 22A includesthe pre-processing of an input signal, and unused inputs, via anorthogonal transformation 2210 to generate a representation of the inputsignal within a finite signal space. The orthogonal transformation 2210may be an orthonormal transformation in certain embodiments. Now thatthe input signal is represented in the finite signal space, the signalis then passed through a communication channel 2230 after which it isprovided to an interference cancellation functional block 2220 that isoperable to perform any of the various embodiments of interferencecancellation described herein. The communication channel 2230 mayintroduce interference. It is noted that the present invention isoperable to perform cancellation of interference of a variety of typesincluding (1) narrowband interference in general, (2) Ham radio, CBradio and HF radio, (3) adjacent channel interference (spillover fromdesired signals in neighboring channels), (4) CDMA on a small number ofcodes, and (5) impulse/burst noise. The present invention envisions anyorthogonal transformation 2210 that is operable to transform an inputsignal into a representation of a finite number of elements within afinite signal space so as to facilitate the interference cancellationaccording to the present invention.

FIG. 22B is a diagram illustrating another embodiment of signaltransformation according to the present invention. The FIG. 22B includesthe pre-processing of an input signal, and unused inputs, via anidentity matrix transformation 2215 to generate a representation of theinput signal within a finite signal space. Again, the orthogonaltransformation 2215 may be an orthonormal transformation in certainembodiments. Now that the input signal is represented in the finitesignal space, the signal is then passed through a communication channel2235 after which it is provided to an interference cancellationfunctional block 2225 that is operable to perform any of the variousembodiments of interference cancellation described herein. Thecommunication channel 2235 may introduce interference. It is again notedthat the present invention is operable to perform cancellation ofinterference of a variety of types including (1) narrowband interferencein general, (2) Ham radio, CB radio and HF radio, (3) adjacent channelinterference (spillover from desired signals in neighboring channels),(4) CDMA on a small number of codes, and (5) impulse/burst noise.Further details are described below with respect to impulse noisecancellation.

Impulse noise is nearly zero most of the time, and large during a fewsamples. For the purpose of analysis only, we consider the rows of theN×N identity matrix as the basis set, where N is the number of samplesper frame (or chips per spreading interval) under consideration. In thisbasis set, each time sample represents one dimension. Hence we see thatthe impulse noise only occupies a small number of dimensions. Thus itcan be canceled by this technique, using an arbitrary basis set, such asthe S-CDMA codes. The adapted de-spreading code has zeros (or nearlyzeros) at the chips corresponding to the time location of the impulsenoise. However, impulse noise occurs at a random, unpredictable locationin each frame. If we know where it is, we can solve the equations forthe weights. But the next frame it will be in a different place. Thismeans re-doing the computations every frame, resulting in highcomplexity.

For low-level impulse noise, it may be difficult to locate the chipsthat are affected by impulse noise. We may use one or more “indicatorcodes” for this purpose, as follows. As an example, say we have 128total codes—for example in the DOCSIS 2.0 situation. We designate 119 ofthese codes as used, or data-carrying codes. We designate 9 of the codesas unused codes, on which numerically-zero-valued symbols aretransmitted. Of these 9 unused codes, 8 codes participate in the linearcombiner for noise cancellation, and there is 1 extra or “indicator”code. The indicator code is de-spread as if it were a used code, thatis, it is given the benefit of the linear combiner canceler. We expectto get a zero symbol at its de-spreader output; if we see noise insteadof zero that provides an indication of the amount of noise that has notbeen canceled. We then proceed as follows to locate the impulse noise.Assume for example that there is one occurrence of impulse noise in agiven symbol, and that the impulse noise affects 8 or fewer chips. Webegin with a set of weights w that null chips 1 through 8 in the timedomain. We use w to de-spread the indicator code, and observe the outputy. We then modify w to null chips 2–9, and again observe y. In a similarmanner, we scan w across the entire symbol, measuring y at each timeoffset. We believe that the power |y|² will exhibit a minimum for theweight set w that corresponds to the time location of the impulse noise.In this manner the location of the impulse noise can be determined. Oncelocated, it can be canceled. An alternative approach would be to observethe sum of squared error signals after making symbol decisions for theused codes, as the window of canceled chip signals is shifted across theblock of chip signals.

FIG. 23 is an operational flow diagram illustrating an embodiment of aninterference cancellation method 2300 that is performed according to thepresent invention. In a block 2310, a spread signal is received thatcontains interference. Then, the received spread signal is de-spreadinto a number of codes in a block 2320. Each of the codes is selectivelyprocessed using linear combination processing as shown in a block 2330.There are a variety of ways in which the linear combination processingmay be performed according to the present invention including using anumber of unused codes, using all of the available codes, and/or usingselected adjacent codes in addition to the unused codes. Ultimately, theinterference cancelled de-spread codes are output as shown in a block2340.

FIG. 24 is an operational flow diagram illustrating another embodimentof an interference cancellation method 2400 that is performed accordingto the present invention. Initially, in some embodiments, the methodinvolves selecting those codes that are to be used as the unused codesas shown in a block 2402. As shown within the FIG. 24, there are threedifferent ways in which this may be performed. They include code matrixreordering, employing null grant periods, and/or zero padding data. Evenother ways are described when referring to the other Figures as well.These will be the codes that are used to perform the linear combining toeffectuate the interference cancellation according to the presentinvention. In even other embodiments as shown in a block 2404, theunused codes (N_(u)) are modulated with numerically zero-valued symbols.Alternatively, the unused codes (N_(u)) may be modulated withnumerically constant-valued symbols that are non-zero without departingfrom the scope and spirit of the invention.

In a block 2410, a spread signal is received that contains interference.Then, the received spread signal is de-spread into a number of codes(N_(c)) as shown in a block 2420. in a block 2430, each of the number ofunused codes (N_(u)) is selectively de-spread. The method then willcontinue to the block 2440 in most instances.

However, in certain embodiments, the method will continue from the block2430 to the block 2432 in which each of the number of preamble codes isselectively de-spread. The preamble symbols are known and can besubtracted once their amplitude and phase have been measured, as shownin a block 2434, for example using a preamble correlator. Thus thepreamble-bearing codes can also be used as inputs to the linear combinerin order to better cancel the interference.

As shown in the block 2440, complex-valued weights for linearcombination processing of the unused codes (N_(u)) are selectivelycalculated. This processing in the block 2440 may be performed byinputting the spread signal, interference, and/or outputs as shown in ablock 2442. In the embodiments where the blocks 2432 and 2434 areperformed, the preamble-bearing codes may be input as shown in a block2444 when performing the processing in the block 2440. The processing inthe block 2440 may be performed be employing LMS processing as shown ina block 2446 and/or LS processing as shown in a block 2448.

Then, in a block 2450, the complex value weights are selectively appliedto scale the unused codes (N_(u)). In a block 2460, the now scaledunused codes (N_(u)) are selectively summed with the desired code.Ultimately, the interference cancelled de-spread codes are output asshown in a block 2440.

FIG. 25 is an operational flow diagram illustrating an embodiment of anunused code selection method 2500 that is performed according to thepresent invention. The question arises whether any subset of the codesis a good choice for the unused codes. We consider the example ofnarrowband interference cancellation in a DOCSIS 2.0 S-CDMA system. Forefficient narrowband interference canceling capability, the unused codeshave to be chosen such that it is possible to combine them in theadapted codes (in the linear combiner) to form one or more notches inthe frequency domain. Thus, for optimal performance, one might need todesignate specific codes as unused. The current DOCSIS 2.0 draftspecification does not permit the selection of which codes are unused.It has been found that successive, or “adjacent”, DOCSIS 2.0 codes arenot a good choice. This is because each code is approximately a shift ofthe previous code. This implies that adjacent or nearly adjacent codeshave nearly the same frequency response. Some techniques that could beused to “force” unused codes at specific rows of the code matrix are thefollowing:

The code matrix may be reordered. In this technique, both the CM andCMTS re-order the code matrix as shown in a block 2510, prior tospreading or de-spreading. This may be performed such that desiredunused codes are grouped together (say at the lower part of therearranged code matrix) as shown in a block 2520. Similarly, the desiredused codes should be grouped as well (say at the upper part of therearranged code matrix) as shown in a block 2530. Using such techniquerequires the knowledge of the reordering pattern at the CMTS as well asall CMs; this may be ensured as shown in a block 2540.

Alternatively, the selection of unused codes may be performed using nullgrant periods. In this technique, the CMTS instructs all CMs to besilent during a specific grant as shown in a block 2505 (i.e., thedesired unused codes). This technique has the advantage that the CMsneed not have prior knowledge of the unused codes and just follow theCMTS grants. However, it may be viewed as causing inefficiencies to theCMTS scheduling process that may prohibit this approach in someimplementations.

Alternatively, the selection of unused codes may be performed byzero-padding the data. In this technique, the CMTS grants the CM alonger grant period that what is needed to transmit the grant data asshown in a block 2555. If desired when performing the operation of theblock 2555, the grant sizes are chosen by the CMTS in a way such thatthe CM zero-padding occurs at the desired unused codes as shown in ablock 2557. The CMTS also instructs the CM to append the transmitteddata with zero-symbols as shown in a block 2565.

FIG. 26 is an operational flow diagram illustrating an embodiment of anS-CDMA interference cancellation method 2600 that is performed accordingto the present invention. In a block 2610, a set of used codes isselected. Then, in a block 2620, a set of unused codes is selected. Asignal is transmitted using the used codes as shown in a block 2630. Incertain embodiments, as shown in a block 2632, we transmit one or morezeroes on the inactive/unused codes. Alternatively, as shown in a block2634, we transmit a known sequence (training or pilot symbols) on theinactive/unused codes. Alternatively, we may transmit lower ordermodulation on “inactive” codes.

Then, in a block 2640, the received signal is processed using thereceived signal's projection on the active (used) codes and the inactive(unused) codes thereby canceling interference. We process the receivedsignal using both its projection onto a desired (active) code, and itsprojection onto the inactive codes, in order to cancel interference onthe desired code. From certain perspectives, in the context of a systemand method that employ vector de-spreading to a spread signal, theprojection may be viewed as being the vector de-spreader output.However, in other contexts, a projection may be viewed as being therepresentation of the received signal across its finite signal space.This understanding of projection may be used to describe therepresentation of the signal across a finite signal space.

The FIG. 26 is performed within the context of an S-CDMA communicationssystem in the presence of interference. There are a number of types ofS-CDMA systems that may support the method of the FIG. 26. For example,some types of S-CDMA systems include DOCSIS 2.0 set of codes andWalsh-Hadamard codes. The selection of the inactive/unused codes may beperformed as illustrated and described above within some of theembodiments shown in a block 2621 including use codes 0, 1, 2, 3, . . .(adjacent codes, as done in DOCSIS 2.0 spec), spacing theinactive/unused codes maximally apart as shown in a block 2622, andselecting the codes according to an optimality criterion as shown in ablock 2623.

For example, when spacing the inactive/unused codes maximally apartwithin DOCSIS 2.0 S-CDMA code set, the 8 unused codes out of 128 totalcodes might be code numbers {15 31 47 63 79 95 111 127}. When selectinga different number of unused codes within the DOCSIS 2.0 S-CDMA codeset, they may be similarly maximally spaced apart.

In addition, the inactive/unused codes may be selected according to theoptimality criterion of the block 2623. Examples of an optimalitycriteria would be to select unused codes include: (1) selectinginactive/unused codes that have maximal correlation with theinterference as shown in a block 2624, (2) minimizing enhancement ofwhite noise resulting from cancellation process as shown in a block2625, and (3) minimizing residual interference power after cancellationas shown in a block 2626.

FIG. 27 is an operational flow diagram illustrating another embodimentof an interference cancellation method 2700 that is performed accordingto the present invention. In a block 2710, a set of active/used basiswaveforms is selected. These basis waveforms may include orthogonal (ornearly orthogonal) waveforms; these waveforms may be viewed as beingsubstantially orthogonal. There are a number of types of sets oforthogonal waveforms may be employed. Some specific examples of sets oforthogonal waveforms include: (1) S-CDMA codes, including DOCSIS 2.0 andWalsh-Hadamard, 2 an orthogonal set of binary spreading codes, (3) anyorthogonal set of quatemary spreading codes, and (4) the rows of theidentity matrix.

Then, in a block 2720, a set of inactive/unused basis waveforms isselected. In certain embodiments as shown in a block 2722, we may assumethat the number of inactive/unused basis waveforms is less than numberof active/used basis waveforms. A signal is transmitted using theactive/used basis waveforms as shown in a block 2730. In certainembodiments, as shown in a block 2732, we transmit one or more zerovalued symbols on the inactive/unused basis waveforms. Alternatively, asshown in a block 2734, we transmit a known sequence (training or pilotsymbols) on the inactive/unused basis waveforms.

Then, in a block 2740, the received signal is processed using thereceived signal's projection on the active (used) basis waveforms andthe inactive (unused) basis waveforms thereby canceling interference. Weprocess the received signal using both its projection onto a desired(active) waveform, and its projection onto the inactive waveforms, inorder to cancel interference on the desired waveform.

Alternatively, in a block 2742, the received signal is processed usingthe received signal's projection on the active (used) basis waveformsthereby canceling interference. We process the received signal using itsprojection onto a desired (active) waveform in order to cancelinterference on the desired waveform.

In even alternative embodiments, in a block 2744, we compute theprojection of the interference on the inactive/unused basis waveforms,and subtract it from the projection on the active/used basis waveformsof the received signal including interference thereby cancelinginterference. It is noted here that we can reduce the computationalcomplexity by computing the null-space projection (the projection of theinterference on the inactive basis waveforms) and subtracting it fromthe overall projection (the projection of the signal+interference on theactive basis waveforms). As an example, if we have 120 active codes and8 inactive codes, in the present method we only need to invert an 8×8matrix. In the standard least-squares approach, we would have to inverta 120×120 matrix.

The selection of the inactive/unused basis waveforms may be performed asillustrated and described above within some of the embodiments selectingadjacent basis waveforms, spacing the inactive/unused basis waveformsmaximally apart, and selecting the basis waveforms according to anoptimality criterion. Examples of an optimality criteria would be toselect unused basis waveforms include: (1) selecting inactive/unusedbasis waveforms that have maximal correlation with the interference, (2)minimizing enhancement of white noise resulting from cancellationprocess, and (3) minimizing residual interference power aftercancellation. These parameters that may be used to perform the selectionof the inactive/unused basis waveforms is analogous to the selection ofthe inactive/unused codes that is performed above with respect to theFIG. 26, except here, the selection is with respect to the basiswaveforms of the signal space.

FIG. 28 is a diagram illustrating an embodiment of a spectrum ofnarrowband interference 2600 that may be addressed and overcome whenpracticing the present invention. The FIG. 28 shows the spectrum ofnarrowband interference (for example, the signal n in the FIGS. 16, 17,and/or 18) that may be present at the input of a communicationsreceiver. The desired signal is not present in this Figure. In thisexample, the 3-dB bandwidth of the interference is 1/32 of the symbolrate of the desired signal. Its power is equal to the desired signal (0dBc), when the desired signal is present. The SNR (Signal to Noise) ofthe desired signal, when present, is 35 dB in the example.

FIG. 29 is a diagram illustrating an embodiment of a spectrum of anadapted code showing a null at a location of interference 2900 that maybe achieved when practicing via the present invention. The FIG. 29 showsthe spectrum of the adapted code. The adapted code is seen to have anull corresponding to the narrowband interference. Hence, the adaptedcode cancels the narrowband interference.

FIG. 30A is a diagram illustrating an embodiment of a receivedconstellation before interference has been cancelled 3000 whenpracticing the present invention. The FIG. 30A shows the output d_(s) ofthe vector de-spreader before interference cancellation is enabled usingthe linear combiner and weight computation functionality. This may beviewed as being the output d_(s) within any of the FIGS. 16, 17, and/or18. That is, all the adaptive weights w_(i) are zero, and only thenormal de-spreading code c_(s) is used to de-spread the desired signal.We see that the signal constellation is unrecognizable due to the largeamount of interference, which has not yet been canceled.

FIG. 30B a diagram illustrating an embodiment of a receivedconstellation after interference has been cancelled 3005 when practicingvia the present invention. The FIG. 30B shows the output d_(s) of thede-spreader after the interference cancellation of the present inventionis enabled using the linear combiner and weight computationfunctionality. Now the adaptive weights w_(i) have adapted and arenonzero, and as a result the adapted de-spreading code c_(a) is used tode-spread the desired signal. We see that the 64 QAM signalconstellation, plus the QPSK constellation used for the preamble, is nowclearly recognizable and the interference has been effectively canceled.

Another variant embodiment of the present invention may be performed byapplying the linear combiner at the chip level instead of the de-spreadsymbol level. In this approach, the 128 chips (again using the 128 codeembodiment example) used in the de-spreader for the desired code areadapted (for example, using the LMS method or LS method) until theyconverge to the near-optimal adapted de-spreading code. This adaptedde-spreading code will be complex-valued and will be a linearcombination of all 128 de-spreading codes. In this approach there are128 adaptive complex weights that need to be trained, so convergence isslower than for the baseline approach in which, for example, only 8weights need to be trained for the 8 unused codes.

The general applicability of the present invention across a wide varietyof contexts is to be understood. The present invention is operable tocancel not only narrowband interference, but any interference thatoccupies a small number of dimensions in the signal space. The firstexample, given above, is narrowband interference. However, other typesof interference may be substantially eliminated according to the presentinvention as well. A narrowband signal occupies a small number of DFTbins (DFT: discrete Fourier transform—one example of an orthonormalexpansion) bins, showing that it occupies a small number of dimensionsin signal space.

An extremely simple example is a CW (Continuous Wave) signal whosefrequency is an integer multiple of the de-spread symbol rate; this CWsignal occupies only a single bin in the DFT, or only one dimension inthe signal space, where each dimension is, in this case, one DFT bin.Another example is a short burst of noise (impulse or burst noise). Ashort burst signal occupies a small number of time samples, againshowing that it too occupies a small number of dimensions, where eachdimension is, in this case, a time sample. Other types of signals can beconstructed without limit that satisfy the property that they occupy asmall number of dimensions. All such signals can be canceled by thepresent technique.

Again, the DFT is just one example of an orthonormal expansion. A secondexample is the code matrix in DOCSIS 2.0 S-CDMA. Innumerable otherorthonormal transforms exist. If a signal occupies a small number ofdimensions in any orthonormal transform, the present invention'stechnique will help cancel it.

The present invention may also be implemented to use unused spatialdimensions to cancel interference according to the present invention.For example, we can generalize the technique to spatial dimensions aswell. One such interpretation of spatial dimensions is with respect toMIMO (multi-input multi-output) systems. We may designate certaintransmit antennas to transmit zeros at certain times. At the receiver,we may also utilize the samples from extra receive antennas to cancelinterference.

In any of the embodiments described herein, the present invention isoperable to store pre-computed weights using any number of variousstorage techniques, such as a look up table (LUT), memory, or some otherstorage technique. This may be beneficial in some cases where it may beimpractical to compute the weights fast enough, so we may want topre-compute some “canned” sets of weights. As an example, consider verywideband interference that occupies ½ the bandwidth of the desiredsignal. Assuming an S-CDMA system, we will need to have 64 unused codesout of 128 total codes. Each desired code now has 64 adaptive weightsthat need to be solved for. This implies a very large matrix to invert,which is very complex to implement in real time. However, we note thatin our favor, there are very few notches of this size (half thebandwidth) to go across the band. If, for example, we pre-compute theweights for several wideband notches and store the weight sets, then wecan simply select the notch that most closely matches the interferencewhen it occurs.

The present invention is also operable to support adjusting and trackingof pre-computed weights. As an extension to the above concept of storingpre-computed weights, we may store a single prototype set of weights,and modify the weights to move the notch around. For example, we canadjust the frequency of the notch without having to completelyre-compute the weights. We can also adjust the depth of the notch. Wecan weight and superimpose pre-computed notches to build up a morecomplex notch structure. We can build a tracking loop that automaticallyadjusts the frequency (or other parameter) of the notch as theinterference changes. Say there is narrowband interference, and we haveapplied a notch that cancels it. Now let the interference slew itsfrequency. We can implement a tracking loop that automatically slews thefrequency location of the notch to track the frequency of theinterference. There are many ways to implement such a tracking loop. Oneway is by taking an FFT of the interference, and tracking the energy inthe peak corresponding to the interference. Another way is to dither thelocation of the notch, and measure the power or SNR at the output. Wethen move the notch in the direction of increasing SNR or decreasinginterference or total power. Many other tracking methods can be devised.

The present invention may also be implemented to perform adjacentchannel interference (ACI) cancellation when performing interferencecancellation. For example, the canceler can also be used to cancel ACI.Consider a desired signal with signals present in the upper and loweradjacent channels. If the adjacent channel signals overlap slightly withthe desired-signal band, ACI results. ACI is in general colored and cantherefore be canceled using the present canceler technique.

In performing the processing, the present invention may employ a slidingwindow. The processing has thus far been described as being done on ablock basis, where a block is typically a symbol of 128 chips in theDOCSIS 2.0 implementation. However, the present invention is alsooperable when employing a sliding block approach as well. This may havethe greatest benefit when the code matrix is the identity matrix, whereno spreading occurs.

Code hopping is defined in the DOCSIS 2.0 spec as a process whereby thecode matrix is modified by a cyclic rotation of the rows of the entirecode matrix (except possibly the all—1's code) on each spreadinginterval. This causes the set of unused codes to be different on eachspreading interval, requiring the re-computation of the adaptive weightsin the canceler on each spreading interval. It would be better to hopover the set of codes excluding the unused codes, so that the unusedcodes will be the same on each spreading interval. This would obviatethe need to re-computation of the adaptive weights on each spreadinginterval, reducing processing complexity. Or, we can just turn off codehopping when the canceler is used. However, this latter approach removesthe benefits of code hopping, which include fairness (equality ofaverage performance) for all users.

In the case of the DOCSIS 2.0 S-CDMA code matrix, the rows, or basisfunctions, are nearly cyclic shifts of each other, with the exception ofcode 0. This property relates adjacent codes to shifts in time by onechip. This in turn relates the linear combiner used on the de-spreaderoutputs to a FIR filter in the time domain. This implies that theadaptive weights for the unused codes are similar to the weights thatare produced by the time domain interference cancellation structure usedfor TDMA. The latter weights can be computed efficiently by the Trenchmethod. Hence we might use the Trench method to compute an initial setof weights for the subspace-based canceler, and iterate the weights to amore exact solution using the LMS or similar tracking method.

In addition, a decision feedback equalizer (DFE)-like structure may alsobe performed, as follows. The canceler begins by using the de-spreaderoutputs of codes 1–8 (for example) in the linear combiner to estimatethe output of the code 9 de-spreader. A hard decision is made on thesymbol from code 9. Now that the symbol on code 9 is available, it canbe used to estimate the symbol on code 10. Once the symbol on code 10 isavailable, it can be used to estimate the symbol on code 11, and so on.A DFE-like structure can be constructed that can run in both directions.

As mentioned and described above, the subspace canceler can be appliedto an arbitrary code matrix (basis set). One such basis set is thediscrete Fourier transform (DFT). In this context one should alsomention the fast DFT methods collectively referred to as the fastFourier transform (FFT). The DFT is not well suited for narrowbandinterference cancellation in the receiver without modifications to thecancellation approach. This is because each basis function, the complextone e^(jnω)(or alternatively written as exp(jnω)), is designed to haveminimal support in the frequency domain. The basis functions cannotcancel a narrowband interferer without very large weights. Instead,locating the canceler predominantly in the transmitter is a betterchoice. One simply does not transmit those tones that overlap with theinterference, designating them as unused “codes” or tones. This approachhas been known in the industry for some time in conjunction withdiscrete multi-tone (DMT) or orthogonal frequency division multiplexing(OFDM) systems.

Moreover, the subspace canceler can be integrated with FEC coding. Inone approach, a Reed-Solomon code can provide parity symbols that aretransmitted on the unused spreading codes instead of zero symbols. Inanother approach, different SNRs may exist on different spreading codes(for example, when spreading code hopping is turned off). In this caseunequal transmitted power may be sent on each spreading code, or unequalnumbers of bits per symbol of modulation. Or, unequal coding strengthcan be used on each spreading code: for example, rate 7/8 on onespreading code and rate 3/4 on another spreading code. An importantpoint is that these approaches will give a better result than codehopping. In code hopping, performance is averaged over all spreadingcodes. It is better to use our prior knowledge of which spreading codesare disadvantaged, and give them more processing power or transmitpower.

The present invention is also operable, when performing interferencecancellation, to perform adjustment of transmitted spectrum to meet adesired spectral mask. It may be desirable to attenuate certain portionsof the spectrum using the subspace canceler. In these applications thecanceler is predominantly located in the transmitter. One example is ina wireless local area network (LAN) applications. Here one has to placea notch in the transmit spectrum at the spectral location of the XMsatellite radio service. The subspace canceler has a great advantageover a notch filter. A notch filter can notch out a designated spectralregion, but in doing so, it distorts the desired signal. The subspacecanceler can create the notch without distorting the desired signal. Thesubspace canceler may also have the following advantage over a notchfilter. A notch filter can cause large excursions in the transmittedpower, whereas the subspace canceler does not.

The interference cancellation according to the present invention mayalso be integrated with pre-coding. The subspace canceler can beintegrated with pre-coding, such as Tomlinson-Harashima pre-coding. Wenote that the subspace canceler can be used for narrowband interferencecancellation and also for equalization of a deep notch in the channel.These are two applications of pre-coding. Hence, if subspacecancellation and pre-coding were combined, would we get some of theadvantages of both.

In view of the above detailed description of the invention andassociated drawings, other modifications and variations will now becomeapparent. It should also be apparent that such other modifications andvariations may be effected without departing from the spirit and scopeof the invention.

1. An apparatus, comprising: a transmitter that produces a spread signalthat includes a numerically constant-valued symbol spread across a firstplurality of codes and data spread across a second plurality of codesand transmits the spread signal across a communication link; a receiverthat receives the spread signal after being transmitted across thecommunication link, the spread signal comprising interference, thereceiver includes: a vector de-spreader that employs the first pluralityof codes and the second plurality of codes to de-spread the spreadsignal; a weight computation functional block that calculates aplurality of complex-valued combining weights using the spread signaland the interference of the spread signal; and a linear combiner thatscales the de-spread signal portions, that are de-spread using the firstplurality of codes, using the plurality of complex-valued combiningweights and combines the scaled, de-spread signal portions that arede-spread using the first plurality of codes and one signal portion thatis de-spread using one code selected from the second plurality of codesto perform interference cancellation on at least one additional signalportion that is de-spread from the spread signal.
 2. The apparatus ofclaim 1, wherein the first plurality of codes includes a plurality ofunused codes; and the second plurality of codes includes a plurality ofused codes.
 3. The apparatus communication system of claim 2, whereinthe first plurality of codes and the second plurality of codes include atotal number of 128 codes; the first plurality of codes includes atleast 8 codes and no more than 32 codes; the second plurality of codesincludes a remaining plurality of codes within the total number of 128codes not included within the first plurality of codes; and theapparatus is DOCSIS (Data Over Cable Service Interface Specification)2.0 S-CDMA (Synchronous Code Division Multiple Access) compliant.
 4. Theapparatus of claim 1, wherein the weight computation functional blockcalculates the plurality of complex-valued combining weights using bothsignal portions that are de-spread from the spread signal using thefirst plurality of codes and signal portions that are de-spread from thespread signal using the second plurality of codes.
 5. The apparatuscommunication system of claim 1, wherein the weight computationfunctional block calculates the plurality of complex-valued combiningweights using codes that are adjacent to the one code selected from thesecond plurality of codes.
 6. The apparatus communication system ofclaim 5, wherein the adjacent codes include two codes immediatelyadjacent to the one code selected from the second plurality of codes. 7.The apparatus of claim 1, wherein the weight computation functionalblock calculates the plurality of complex-valued combining weights usingat least one of signal portions that are de-spread from the spreadsignal using the first plurality of codes and signal portions that arede-spread from the spread signal using the second plurality of codesthat bear predetermined symbols.
 8. The apparatus of claim 1, whereinthe weight computation functional block employs at least one of leastmeans square processing and least square processing to calculate theplurality of complex-valued combining weights.
 9. The apparatus of claim1, wherein the receiver is operable to demodulate the spread signalusing at least one of Binary Phase Shift Keying (BPSK), Quadrature PhaseShift Keying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.
 10. The apparatusof claim 1, wherein the apparatus is at least one of a multi-channelheadend physical layer burst receiver, a single chip wireless modem, asingle chip DOCSIS (Data Over Cable Service InterfaceSpecification)/EuroDOCSIS cable modem, a base station receiver, a mobilereceiver, a satellite earth station, a tower receiver, a high definitiontelevision set top box receiver, and a transceiver.
 11. An apparatus,comprising: a vector de-spreader that employs a first plurality of codesand a second plurality of codes to de-spread a spread signal, the spreadsignal includes interference; a weight computation functional block thatcalculates a plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and a linearcombiner that scales the de-spread signal portions, that are de-spreadusing the first plurality of codes, using the plurality ofcomplex-valued combining weights and combines the scaled, de-spreadsignal portions that are de-spread using the first plurality of codesand one signal portion that is de-spread using one code selected fromthe second plurality of codes to perform interference cancellation on atleast one additional signal portion that is de-spread from the spreadsignal.
 12. The apparatus of claim 11, wherein the first plurality ofcodes includes a plurality of unused codes; and the second plurality ofcodes includes a plurality of used codes.
 13. The apparatus of claim 12,wherein the first plurality of codes and the second plurality of codesinclude a total number of 128 codes; the first plurality of codesincludes at least 8 codes and no more than 32 codes; the secondplurality of codes includes a remaining plurality of codes within thetotal number of 128 codes not included within the first plurality ofcodes; and the apparatus is DOCSIS (Data Over Cable Service InterfaceSpecification) 2.0 S-CDMA (Synchronous Code Division Multiple Access)compliant.
 14. The apparatus of claim 11, wherein the weight computationfunctional block calculates the plurality of complex-valued combiningweights using both signal portions that are de-spread from the spreadsignal using the first plurality of codes and signal portions that arede-spread from the spread signal using the second plurality of codes.15. The apparatus of claim 11, wherein the weight computation functionalblock calculates the plurality of complex-valued combining weights usingcodes that are adjacent to the one code selected from the secondplurality of codes.
 16. The apparatus of claim 15, wherein the adjacentcodes include two codes immediately adjacent to the one code selectedfrom the second plurality of codes.
 17. The apparatus of claim 11,wherein the weight computation functional block calculates the pluralityof complex-valued combining weights using at least one of signalportions that are de-spread from the spread signal using the firstplurality of codes and signal portions that are de-spread from thespread signal using the second plurality of codes that bearpredetermined symbols.
 18. The apparatus of claim 11, wherein the weightcomputation functional block employs at least one of least means squareprocessing and least square processing to calculate the plurality ofcomplex-valued combining weights.
 19. The apparatus of claim 11, whereinthe apparatus includes a communication receiver that is operable todemodulate the spread signal using at least one of Binary Phase ShiftKeying (BPSK), Quadrature Phase Shift Keying (QPSK), 8 QuadratureAmplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM,516 QAM, and 1024 QAM.
 20. The apparatus of claim 11, wherein theapparatus is at least one of a multi-channel headend physical layerburst receiver, a single chip wireless modem, a single chip DOCSIS (DataOver Cable Service Interface Specification)/EuroDOCSIS cable modem, abase station receiver, a mobile receiver, a satellite earth station, atower receiver, a high definition television set top box receiver, and atransceiver.
 21. An apparatus, comprising: a vector de-spreader thatemploys a first plurality of codes and a second plurality of codes tode-spread a spread signal; a weight computation functional block thatcalculates a plurality of complex-valued combining weights using thespread signal and interference contained within the spread signal; alinear combiner that scales the de-spread signal portions, that arede-spread using the first plurality of codes, using the plurality ofcomplex-valued combining weights and selectively sums the scaled,de-spread signal portions that are de-spread using the first pluralityof codes and one signal portion that is de-spread using one codeselected from the second plurality of codes to perform interferencecancellation on at least one additional signal portion that is de-spreadfrom the spread signal; and an iterative adaptive weight functionalblock that is operable to perform error calculation of a hard decisioncorresponding to the at least one signal portion of the spread signal;and wherein the iterative adaptive weight functional block updates theplurality of complex-valued combining weights using the calculatederror.
 22. The apparatus of claim 21, wherein the iterative adaptiveweight functional block performs least means square error processing tocalculate the error that is used to update the plurality ofcomplex-valued combining weights.
 23. The apparatus of claim 21, whereinthe first plurality of codes includes a plurality of unused codes; andthe second plurality of codes includes a plurality of used codes. 24.The apparatus of claim 21, wherein the apparatus includes acommunication receiver that is operable to demodulate the signal usingat least one of Binary Phase Shift Keying (BPSK), Quadrature Phase ShiftKeying (QPSK), 8 Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM,64 QAM, 128 QAM, 256 QAM, 516 QAM, and 1024 QAM.
 25. The apparatus ofclaim 21, wherein the apparatus is at least one of a multi-channelheadend physical layer burst receiver, a single chip wireless modem, asingle chip DOCSIS (Data Over Cable Service InterfaceSpecification)/EuroDOCSIS cable modem, a base station receiver, a mobilereceiver, a satellite earth station, a tower receiver, a high definitiontelevision set top box receiver, and a transceiver.
 26. An apparatus,comprising: a transmitter that is operable to produce a spread signalthat includes a first symbol spread across a first plurality of codesand a second symbol spread across a second plurality of codes and thatis operable to transmit the spread signal across a communication link;wherein the first symbol has a first modulation type and the secondsymbol has a second modulation type such that the first modulation typeis of a lower-order modulation type than the second modulation type; areceiver that is operable to receive the spread signal after beingtransmitted across the communication link, the spread signal received atthe receiver including interference, the receiver comprising: a vectorde-spreader that is operable to employ the first plurality of codes andthe second plurality of codes to de-spread the spread signal; and alinear combiner that is operable to scale the de-spread signal portions,that are de-spread using the first plurality of codes, using a pluralityof complex-valued combining weights and that is operable to combine thescaled, de-spread signal portions that are de-spread using the firstplurality of codes and one signal portion that is de-spread using onecode selected from the second plurality of codes to perform interferencecancellation on at least one additional signal portion that is de-spreadfrom the spread signal.
 27. The apparatus of claim 26, wherein: thefirst plurality of codes includes a plurality of unused codes; and thesecond plurality of codes includes a plurality of used codes.
 28. Theapparatus of claim 26, wherein: the first plurality of codes includes aplurality of unused codes; the second plurality of codes includes aplurality of used codes; the first plurality of codes and the secondplurality of codes include a total number of 128 codes; the firstplurality of codes includes at least 8 codes and no more than 32 codes;the second plurality of codes includes a remaining plurality of codeswithin the total number of 128 codes not included within the firstplurality of codes; and the apparatus is a DOCSIS (Data Over CableService Interface Specification) 2.0 S-CDMA (Synchronous Code DivisionMultiple Access) compliant.
 29. The apparatus of claim 26, furthercomprising: a weight computation functional block that is operable tocalculate the plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and wherein theweight computation functional block is operable to calculate theplurality of complex-valued combining weights using both signal portionsthat are de-spread from the spread signal using the first plurality ofcodes and signal portions that are de-spread from the spread signalusing the second plurality of codes.
 30. The apparatus of claim 26,further comprising: a weight computation functional block that isoperable to calculate the plurality of complex-valued combining weightsusing the spread signal and the interference of the spread signal; andwherein the weight computation functional block is operable to calculatethe plurality of complex-valued combining weights using codes that areadjacent to the one code selected from the second plurality of codes.31. The apparatus of claim 26, further comprising: a weight computationfunctional block that is operable to calculate the plurality ofcomplex-valued combining weights using the spread signal and theinterference of the spread signal; wherein the weight computationfunctional block is operable to calculate the plurality ofcomplex-valued combining weights using codes that are adjacent to theone code selected from the second plurality of codes; and wherein theadjacent codes include two codes immediately adjacent to the one codeselected from the second plurality of codes.
 32. The apparatus of claim26, further comprising: a weight computation functional block that isoperable to calculate the plurality of complex-valued combining weightsusing the spread signal and the interference of the spread signal; andwherein the weight computation functional block is operable to calculatethe plurality of complex-valued combining weights using at least one ofsignal portions that are de-spread from the spread signal using thefirst plurality of codes and signal portions that are de-spread from thespread signal using the second plurality of codes that bearpredetermined symbols.
 33. The apparatus of claim 26, furthercomprising: a weight computation functional block that is operable tocalculate the plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and wherein theweight computation functional block is operable to employ at least oneof least means square processing and least square processing tocalculate the plurality of complex-valued combining weights.
 34. Theapparatus of claim 26, wherein: the receiver is operable to demodulatethe spread signal using at least one of Binary Phase Shift Keying(BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature AmplitudeModulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and1024 QAM.
 35. The apparatus of claim 26, wherein: the receiver is atleast one of a multi-channel headend physical layer burst receiver, asingle chip wireless modem, a single chip DOCSIS (Data Over CableService Interface Specification)/EuroDOCSIS cable modem, a base stationreceiver, a mobile receiver, a satellite earth station, a towerreceiver, a high definition television set top box receiver, and atransceiver.
 36. The apparatus of claim 26, wherein: the receiver isoperable to select the first plurality of codes and the second pluralityof codes; and the receiver is operable to provide this selectioninformation to the transmitter via the communication link.
 37. Theapparatus of claim 26, wherein: the first plurality of codes a pluralityof unused codes; the second plurality of codes includes a plurality ofused codes; the receiver is operable to grant null grants to thetransmitter; and the transmitter is operable to employ the null grantsas the plurality of unused codes.
 38. The apparatus of claim 26,wherein: the receiver is operable to grant the transmitter a grantperiod that is longer than the transmitter requires to transmit the datasymbol; and the transmitter is operable to select the first plurality ofcodes and the second plurality of codes by zero-padding the data symbol.39. The apparatus of claim 26, wherein: the plurality of complex-valuedcombining weights is a plurality of pre-computed complex-valuedcombining weights; the receiver includes a memory from which theplurality of pre-computed complex-valued combining weights is retrieved;and a linear combiner that is operable to scale the de-spread signalportions, that are de-spread using the first plurality of codes, usingthe plurality of complex-valued combining weights and is operable tocombine the scaled, de-spread signal portions that are de-spread usingthe first plurality of codes and one signal portion that is de-spreadusing one code selected from the second plurality of codes to performinterference cancellation on at least one additional signal portion thatis de-spread from the spread signal.
 40. The apparatus of claim 26,wherein: the first symbol is a preamble symbol; and the second symbol isa data symbol.
 41. The apparatus of claim 26, further comprising: aweight computation functional block that is operable to calculate theplurality of complex-valued combining weights using the spread signaland the interference of the spread signal.
 42. The apparatus of claim26, wherein: the interference is substantially colored; and theinterference cancellation involves performing adjacent channelinterference (ACI) cancellation.
 43. The apparatus of claim 26, wherein:the first plurality of codes and the second plurality of codes form aplurality of available codes; the first plurality of codes includes aplurality of unused codes; the second plurality of codes includes aplurality of used codes; and the plurality of unused codes includes atleast one of a plurality of adjacent codes and a plurality of maximallyspaced apart codes within the plurality of available codes.
 44. Anapparatus, comprising: a transmitter that is operable to produce aspread signal that includes a first symbol spread across a firstplurality of codes and a second symbol spread across a second pluralityof codes and that is operable to transmit the spread signal across acommunication link; wherein the first plurality of codes and the secondplurality of codes are arranged into a code matrix; wherein, within thetransmitter, the code matrix is reordered from its original order to amodified order according to a predetermined reordering pattern beforethe predetermined symbol is spread across a first plurality of codes andthe data symbol is spread across a second plurality of codes; areceiver, communicatively coupled to the transmitter via thecommunication link, that receives the spread signal after beingtransmitted across the communication link, the spread signal comprisinginterference, the receiver comprising: a vector de-spreader that isoperable to employ the first plurality of codes and the second pluralityof codes to de-spread the spread signal; wherein, within the receiver,the code matrix is reverse reordered from its modified order to theoriginal order according to the predetermined reordering pattern beforethe vector de-spreader employs the first plurality of codes and thesecond plurality of codes to de-spread the spread signal; and a linearcombiner that is operable to scale the de-spread signal portions, thatare de-spread using the first plurality of codes, using the plurality ofcomplex-valued combining weights and that is operable to combine thescaled, de-spread signal portions that are de-spread using the firstplurality of codes and one signal portion that is de-spread using onecode selected from the second plurality of codes to perform interferencecancellation on at least one additional signal portion that is de-spreadfrom the spread signal.
 45. The apparatus of claim 44, wherein: thefirst plurality of codes includes a plurality of unused codes; and thesecond plurality of codes includes a plurality of used codes.
 46. Theapparatus of claim 44, wherein: the first plurality of codes includes aplurality of unused codes; the second plurality of codes includes aplurality of used codes; the first plurality of codes and the secondplurality of codes include a total number of 128 codes; the firstplurality of codes includes at least 8 codes and no more than 32 codes;the second plurality of codes includes a remaining plurality of codeswithin the total number of 128 codes not included within the firstplurality of codes; and the apparatus is DOCSIS (Data Over Cable ServiceInterface Specification) 2.0 S-CDMA (Synchronous Code Division MultipleAccess) compliant.
 47. The apparatus of claim 44, further comprising: aweight computation functional block that is operable to calculate theplurality of complex-valued combining weights using the spread signaland the interference of the spread signal; and wherein the weightcomputation functional block is operable to calculate the plurality ofcomplex-valued combining weights using both signal portions that arede-spread from the spread signal using the first plurality of codes andsignal portions that are de-spread from the spread signal using thesecond plurality of codes.
 48. The apparatus of claim 44, furthercomprising: a weight computation functional block that is operable tocalculate the plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and wherein theweight computation functional block is operable to calculate theplurality of complex-valued combining weights using codes that areadjacent to the one code selected from the second plurality of codes.49. The apparatus of claim 44, further comprising: a weight computationfunctional block that is operable to calculate the plurality ofcomplex-valued combining weights using the spread signal and theinterference of the spread signal; wherein the weight computationfunctional block is operable to calculate the plurality ofcomplex-valued combining weights using codes that are adjacent to theone code selected from the second plurality of codes; and wherein theadjacent codes include two codes immediately adjacent to the one codeselected from the second plurality of codes.
 50. The apparatus of claim44, further comprising: a weight computation functional block that isoperable to calculate the plurality of complex-valued combining weightsusing the spread signal and the interference of the spread signal; andwherein the weight computation functional block is operable to calculatethe plurality of complex-valued combining weights using signal portionsfrom at least one of signal portions that are de-spread from the spreadsignal using the first plurality of codes and the signal portions thatare de-spread from the spread signal using second plurality of codesthat bear predetermined symbols.
 51. The apparatus of claim 44, furthercomprising: a weight computation functional block that is operable tocalculate the plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and wherein theweight computation functional block is operable to employ at least oneof least means square processing and least square processing tocalculate the plurality of complex-valued combining weights.
 52. Theapparatus of claim 44, wherein: the receiver is operable to demodulatethe spread signal using at least one of Binary Phase Shift Keying(BPSK), Quadrature Phase Shift Keying (QPSK), 8 Quadrature AmplitudeModulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM, 256 QAM, 516 QAM, and1024 QAM.
 53. The apparatus of claim 44, wherein: the receiver is atleast one of a multi-channel headend physical layer burst receiver, asingle chip wireless modem, a single chip DOCSIS (Data Over CableService Interface Specification)/EuroDOCSIS cable modem, a base stationreceiver, a mobile receiver, a satellite earth station, a towerreceiver, a high definition television set top box receiver, and atransceiver.
 54. The apparatus of claim 44, wherein: the receiver isoperable to select the first plurality of codes and the second pluralityof codes; and the receiver is operable to provide this selectioninformation to the transmitter via the communication link.
 55. Theapparatus of claim 44, wherein: the first plurality of codes includes aplurality of unused codes; the second plurality of codes includes aplurality of used codes; the receiver is operable to grant null grantsto the transmitter; and the transmitter is operable to employ the nullgrants as the plurality of unused codes.
 56. The apparatus of claim 44,wherein: the receiver is operable to grant the transmitter a grantperiod that is longer than the transmitter requires to transmit the datasymbol; and the transmitter is operable to select the first plurality ofcodes and the second plurality of codes by zero-padding the data symbol.57. The apparatus of claim 44, wherein: the plurality of complex-valuedcombining weights is a plurality of pre-computed complex-valuedcombining weights; the receiver includes a memory from which theplurality of pre-computed complex-valued combining weights is retrieved;and the linear combiner is operable to scale the de-spread signalportions, that are de-spread using the first plurality of codes, usingthe plurality of complex-valued combining weights and is operable tocombine the scaled, de-spread signal portions that are de-spread usingthe first plurality of codes and one signal portion that is de-spreadusing one code selected from the second plurality of codes to performinterference cancellation on at least one additional signal portion thatis de-spread from the spread signal.
 58. The apparatus of claim 44,wherein: the first symbol is a preamble symbol; and the second symbol isa data symbol.
 59. The apparatus of claim 44, further comprising: aweight computation functional block that is operable to calculate theplurality of complex-valued combining weights using the spread signaland the interference of the spread signal; and wherein the weightcomputation functional block is operable to calculate the plurality ofcomplex-valued combining weights using the spread signal and theinterference of the spread signal.
 60. The apparatus of claim 44,wherein: the interference is substantially colored; and the interferencecancellation involves performing adjacent channel interference (ACI)cancellation.
 61. The apparatus of claim 44, wherein: the firstplurality of codes and the second plurality of codes form a plurality ofavailable codes; the first plurality of codes includes a plurality ofunused codes; the second plurality of codes includes a plurality of usedcodes; and the plurality of unused codes includes at least one of aplurality of adjacent codes and a plurality of maximally spaced apartcodes within the plurality of available codes.
 62. An apparatus,comprising: a vector de-spreader that is operable to employ a firstplurality of codes and a second plurality of codes to de-spread a spreadsignal that includes a first symbol that has been spread across thefirst plurality of codes and a second symbol that has been spread acrossthe second plurality of codes; a memory that includes a plurality ofpre-computed complex-valued combining weights; and a linear combinerthat is operable to scale the de-spread signal portions, that arede-spread using the first plurality of codes: using the plurality ofpre-computed complex-valued combining weights and that is operable tocombine the scaled, de-spread signal portions that are de-spread usingthe first plurality of codes and one signal portion that is de-spreadusing one code selected from the second plurality of codes to performinterference cancellation on at least one additional signal portion thatis de-spread from the spread signal.
 63. The apparatus of claim 62,wherein: the communication receiver is communicatively coupled to acommunication transmitter via a communication link; and thecommunication transmitter is operable to produce the spread signal thatincludes the first symbol spread across the first plurality of codes andthe second symbol spread across the second plurality of codes and isoperable to transmit the spread signal across the communication link.64. The apparatus of claim 62, wherein: the first symbol has a firstmodulation type and the second symbol has a second modulation type suchthat the first modulation type is of a lower-order modulation type thanthe second modulation type.
 65. The apparatus of claim 62, furthercomprising: a weight computation functional block that is operable tocalculate a plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and wherein thelinear combiner is operable to scale the de-spread first plurality ofcodes using the plurality of complex-valued combining weights and isoperable to combine the scaled first plurality of codes and one codeselected from the second plurality of codes to perform interferencecancellation on at least one code that is from the spread signal. 66.The apparatus of claim 62, further comprising: a weight computationfunctional block that is operable to modify the plurality ofpre-computed complex-valued combining weights based on the spread signaland the interference of the spread signal; and wherein the linearcombiner is operable to scale the first plurality of codes using themodified plurality of pre-computed complex-valued combining weights andis operable to combine the scaled first plurality of codes and one codeselected from the second plurality of codes to perform interferencecancellation on at least one code that is from the spread signal. 67.The apparatus of claim 62, wherein: the first plurality of codesincludes a plurality of unused codes; and the second plurality of codesincludes a plurality of used codes.
 68. The apparatus of claim 62,wherein: the first plurality of codes includes a plurality of unusedcodes; the second plurality of codes includes a plurality of used codes;the first plurality of codes and the second plurality of codes include atotal number of 128 codes; the first plurality of codes includes atleast 8 codes and no more than 32 codes; the second plurality of codesincludes a remaining plurality of codes within the total number of 128codes not included within the first plurality of codes; and theapparatus is DOCSIS (Data Over Cable Service Interface Specification)2.0 S-CDMA (Synchronous Code Division Multiple Access) compliant. 69.The apparatus of claim 62, further comprising: a weight computationfunctional block that is operable to calculate a plurality ofcomplex-valued combining weights using the spread signal and theinterference of the spread signal; and wherein the weight computationfunctional block is operable to calculate the plurality ofcomplex-valued combining weights using both signal portions that arede-spread from the spread signal using the first plurality of codes andsignal portions that are de-spread from the spread signal using thesecond plurality of codes.
 70. The apparatus of claim 62, furthercomprising: a weight computation functional block that is operable tocalculate a plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and wherein theweight computation functional block is operable to calculate theplurality of complex-valued combining weights using codes that areadjacent to the one code selected from the second plurality of codes.71. The apparatus of claim 62, further comprising: a weight computationfunctional block that is operable to calculate a plurality ofcomplex-valued combining weights using the spread signal and theinterference of the spread signal; wherein the weight computationfunctional block is operable to calculate the plurality ofcomplex-valued combining weights using codes that are adjacent to theone code selected from the second plurality of codes; and wherein theadjacent codes include two codes immediately adjacent to the one codeselected from the second plurality of codes.
 72. The apparatus of claim62, further comprising: a weight computation functional block that isoperable to calculate a plurality of complex-valued combining weightsusing the spread signal and the interference of the spread signal; andwherein the weight computation functional block is operable to calculatethe plurality of complex-valued combining weights using codes from atleast one of signal portions that are de-spread from the spread signalusing the first plurality of codes and signal portions that arede-spread from the spread signal using the second plurality of codesthat bear predetermined symbols.
 73. The apparatus of claim 62, furthercomprising: a weight computation functional block that is operable tocalculate a plurality of complex-valued combining weights using thespread signal and the interference of the spread signal; and wherein theweight computation functional block is operable to employ at least oneof least means square processing and least square processing tocalculate the plurality of complex-valued combining weights.
 74. Theapparatus of claim 62, wherein: the apparatus includes a receiver thatis operable to demodulate the spread signal using at least one of BinaryPhase Shift Keying (BPSK), Quadrature Phase Shift Keying (QPSK), 8Quadrature Amplitude Modulation (QAM), 16 QAM, 32 QAM, 64 QAM, 128 QAM,256 QAM, 516 QAM, and 1024 QAM.
 75. The apparatus of claim 62, wherein:the apparatus is at least one of a multi-channel headend physical layerburst receiver, a single chip wireless modem, a single chip DOCSIS (DataOver Cable Service Interface Specification)/EuroDOCSIS cable modem, abase station receiver, a mobile receiver, a satellite earth station, atower receiver, a high definition television set top box receiver, and atransceiver.
 76. The apparatus of claim 62, wherein: the receiver isoperable to select the first plurality of codes and the second pluralityof codes; and the receiver is operable to provide this selectioninformation to the transmitter via the communication link.
 77. Theapparatus of claim 62, wherein: the first plurality of codes includes aplurality of unused codes; the second plurality of codes includes aplurality of used codes; the receiver is operable to grant null grantsto the transmitter; and the transmitter is operable to employ the nullgrants as the plurality of unused codes.
 78. The apparatus of claim 62,wherein: the receiver is operable to grant the transmitter a grantperiod that is longer than the transmitter requires to transmit the datasymbol; and the transmitter is operable to select the first plurality ofcodes and the second plurality of codes by zero-padding the data symbol.79. The apparatus of claim 62, wherein: the first symbol is a preamblesymbol; and the second symbol is a data symbol.
 80. The apparatus ofclaim 62, further comprising: a weight computation functional block thatis operable to calculate the plurality of complex-valued combiningweights using the spread signal and the interference of the spreadsignal.
 81. The apparatus of claim 62, wherein: the interference issubstantially colored; and the interference cancellation involvesperforming adjacent channel interference (ACI) cancellation.
 82. Theapparatus of claim 62, wherein: the first plurality of codes and thesecond plurality of codes form a plurality of available codes; the firstplurality of codes comprises a plurality of unused codes; the secondplurality of codes comprises a plurality of used codes; and theplurality of unused codes includes at least one of a plurality ofadjacent codes and a plurality of maximally spaced apart codes withinthe plurality of available codes.